Microtan 65 Review

Microtan_65_001

Just another 6502 system? We think not. Microtan’s expandability is almost second to none and it could be a winner.

By Henry Budgett

The ideal system in most people’s minds is one that is as cheap as possible, provides the most facilities, is expandable to the limits of its design and can be obtained piece by piece as the money is saved. Up to now there have been several systems that have sought to achieve these varied aims, and the results have been many and varied.

The machine reviewed here is another contender in this field and certainly seems to be set for success where others have not. Based on the 6502 CPU, the same chip as used in PET and Apple among others, it has several very interesting items to offer.

Concept of A System

The usefulness of a computer on a board is limited, the usefulness of a system with attendant peripherals is much greater. The ideal balance is struck when the single board can become part of a system and thus have the capability of fulfilling the needs of both markets.

Microtan has been designed in this way, the complete system has been planned and is then offered board by board. This review is only going to cover the basic board but mention will be made of the available expansion to construct the system. Table 1 gives details of the various stages that are available, in their various configured forms.

Assembly Or Assembled?

I built the Microtan from a kit, something that I believe is worth doing as you not only save money but you do get an insight into how the hardware is strung together.

Presentation is superb and to anyone who is competent with a soldering iron this should represent no more than an evening’s work. Please note that the PCB is double sided and through-hole-plated so you must use a fine tip on the iron and fine solder otherwise you will have problems.

The manual that is supplied covers all the areas needed to construct the kit and get it up and running. It covers other areas that I will mention later. The only serious omission is the lack of a circuit diagram, but this is being rectified I gather. You will need a power supply, the 5 volt supply that we published in CT serves admirably or you can buy one from Tangerine.

The true test of any kit is whether it works, it did in its basic format and with the graphics option in place but it died when I tried to add the lower case option. Immediate thoughts of dead ROMs were not correct, the eventual culprit was a tri-state device that was permanently tri-stated. Quick work by Tangerine meant that I was back on the screen before the postman had called twice.

Micro Monitor

The old question of “How much can you fit into a pint pot?” rears its ugly head with Tanbug, the 1K monitor supplied as standard. The answer in this case is “Enough!”. At this stage you have a system that can only deal with machine code and a glance at Table 2 will show that there is only one possible omission from the monitor, that of cassette handling. Well, you don’t have a cassette interface yet so what are you worrying about? If you are going to expand to Tanex, which has that necessary interface, you get the routine for handling named files which you can either load up yourself or get in an EPROM that plugs in to a socket and is called through Tanbug. The cassette handling is at a choice of 300 or 4800 Baud so you can’t even boil the kettle let alone drink a cup of coffee while loading programs.

What does Tanbug have that sets it apart from other monitors? Two things really, you get a full listing of the firmware with notes and explanations and you don’t get any bugs, at least I haven’t found any yet. It does all that the Microtan user will require and if you ever get big enough to warrant it there is a bigger version called XBUG lurking in a dark corner.

Manual Means Handy?

The little orange covered book that is supplied is worthy of a mention in its own right. OK, it’s not perfect but it is detailed and concise. One or two errors have escaped correction but nothing that will cause the crashing of programs or other damage. The book fits into a ring binder and will be joined by the manuals for Tanex and the other family members, a neat concept in its own way.

For a change the manual is logical, it explains the concept of the board, then the system, then the details of the 6502 with the complete instruction set and then a very detailed chapter on the monitor and its uses – complete with the listing and finally it gives you a couple of games. It is essential to read the whole thing through from cover to cover before starting to play, the unit is complex and should be understood before anything is attempted.

What You Get

Once the board is built and the manual read you are ready to go. All you need now is a black and white TV and a 5 volt power supply at about 1 amp. Connect up, turn on and hit reset. The screen is covered in a pretty pattern with the words TANBUG at the bottom followed by a prompt character. At this point we find the only serious problem with the system. You have a ? on the screen but you are told that you should have a square blob, have you blown it up? No, you haven’t got the lower case option. It is explained in the manual but it is very unclear and has caused much confusion and alarm both in the office and outside.

So, you have a working system. Machine code programmers can now go and have a ball, the rest of us start learning. If you are a dedicated BASIC person Tanex is a must, throw away the Hex keypad (superb thought it is), plug in the full ASCII, the system works out which you are using, and let yourself go with a 10K Microsoft BASIC.

Points worth of note, and praise, are the rock steady display on your TV, the VDU RAM is only accessed when the system RAM is not so you don’t get the usual flicker, the excellent Hex keypad and the almost unbelievable packing density. Because the system is based around the 6502 comparisons with the Acorn, reviewed in August 79, are almost inevitable. With Microtan you get a proper VDU as opposed to an LED display, a decent keypad that is separate and a slightly more powerful monitor but you do lose the cassette (at this stage).

The Guts Of The Matter

Figure_001

Fig.1. Microtan’s architecture, all on one board to!

Because of a lack of space on the board certain apparently ignored features are implemented at other points in the system. Figure 1 shows the architecture of the board, the keyboard interface is intelligent in that it detects what type is being used. The memory map of the system, see Fig.2, appears to be rather limited, full decoding is done on the Tanex board and gives the map shown in Figure 3. This is not the disadvantage that it might appear to be, it allows the contents of RAM on Microtan to be protected against DMA as are the I/O ports and the ROM area. Whilst on the subject of I/O it is worth noting that you get a 1K area that is addressable as I/O, this compares with a maximum of 256 on devices using the Z80 or 8080.

Figure_002

Fig.2. The simple memory map produced by Microtan

Figure_003

Fig.3. Once you’ve added Tanex you get a proper memory map, which is fairly impressive.

The system expansion is shown in Figure 4, full details of the bus structure are given along with notes for DIY people. The address bus buffer chips are supplied as part of the Tanex unit, so don’t worry about the empty sockets.

Figure_004

Fig.4. How you expand through Tanbus

On Board Options

Despite the fact that the basic Microtan packs in a 6502, keyboard interface, VDU, 1K of RAM and 1K of monitor ROM there is more to come! As seen from the previously mentioned Fig.4 the address bus buffers fit on, but that’s not the end. You can have lower case alphabetics, not essential at this stage, and pixel type graphics, sometimes called “high resolution” but really made up of little squares not dots. Tangerine are quite honest about them and call them “Chunky” which is a very apt description, they are good enough for Teletext simulations and games etc.

Because of the ingenious VDU design it is quite possible to run a program that actually resides in the screen memory without bombing everything, try that on your system.

Expanding Horizons

Glancing back to Table 1 you can see the basis of your system emerging. The rest is coming shortly and completes the story. Tanram will be the next board to go on sale and offers 40K of memory on a single board and this will have the capability of bank selection so RAM freaks can have the odd megabyte or six if they want. You may have realised that the system is now full, see Fig.3. Next on the stocks is Tandisc, offering you the floppies that you dream of, up to four double density units are planned.

Microtan_65_004

The Microtan board installed in the mini-rack

Microtan_65_003

Tanex fits on top in the mini-rack system, along with the power supply and Hex keyboard.

Housing all this exotic hardware need not be a problem either, the case that Tangerine supply will hold Microtan and Tanex complete with power supply. The other style that you could use is a card frame, I am building my system in a Vero unit, assembled from System KM4C parts which also offer such goodies as front panels and modules. However you could design your system to fit into a VDU case and have a self-contained system, it’s up to you.

Microtan_65_002

The author’s system growing inside a Vero rack.

Summing Up

Microtan, and its attendant extras, offer the first time buyer a low cost entry point into computing. Taking a boxed two-board system with all the options, power supply and key board you have a more powerful unit than a PET, it has more I/O capability and at £350 it is a lot cheaper!

The product appears to have been launched with a great deal of thought and planning, in itself a change from some rivals, and seems to have found a niche in the market almost overnight. The only thing it hasn’t got is a “second generation” CPU such as a Z80 or 6809 but that doesn’t seem to be too much of a handicap, the dedicated machine code programmers among you might disagree but no-one else has!

Table 1. The various system configurations for Microtan
Board Microtan 65
Features 6502, 1K RAM, 1K ROM, 6 I/O ports
Options Pixel graphics, lower case alphas, address bus buffers
Need to run TV, Hex keypad, 5V PSU @ 1A

 

Board Tanex
Features 1K RAM, 16 parallel I/O, TTL serial I/O, cassette I/O, 2 by 16 bit counter timers, full memory map, data bus buffers
Options 6K RAM, 4K ROM, 10K Microsoft BASIC, double above I/O plus RS232/20 mA serial with full modem control

 

Board Tanram
Features 40K mixed static and dynamic RAM

 

Board Tandisc
Features Control of four drives
Extras Motherboard, case, power supply, Hex keypad, ASCII keyboard

 

Table. 2 The available monitor commands on Tanbug
Monitor Command Function
M(add)(term) Modify memory locations, terminator type allows step through, cancel or jump out.
L(add),(numb)(term) Lists the contents of specified memory locations in tabular form.
G(add)(term) Sets internal registers and executes program at address given. NB cursor disappears.
R Sets memory modify command to register mode. Allows the 6502s internal registers to be altered.
S Sets single step mode, see P & N
N Resets to normal mode from single step
P Causes monitor to execute next instruction, can be set to execute n instructions. Gives display of all registers and returns to monitor.
B(add),(numb)(term) Sets breakpoint at specified address, up to eight are allowed. All registers are displayed and P command may be sued to continue.
O(branch add)(dest add)(term) Calculates offsets between specified addresses for use in branch arguments.
C(start add)(end add)(start add dest)(term) NB (term) can be CR, LF or SP Copies memory locations and blocks.

 First published in Computing Today magazine, June 1980

Samson Reviewed

Samson-1_001

Underneath a new exterior the Samson reveals itself as an original ‘Mighty Micro’.

By John Fitzgerald

When the Editor slipped me a Samson-1 with a request to review it, I wondered what I was getting. It was a pleasant surprise to discover that the Samson is just a Sym-1 in a smart plastic case. I had played with a Sym for a few days some months before and was pleased to get my hands on one again. If you are thinking of spending your hard-earned cash on one of these space-age toys, you need to know one thing. Is it any good? I am happy to report that the Samson is good – very good.

The Samson-1

For the technically minded, a functional block diagram of the system (Fig.1) shows the major hardware features of the Samson and indicates some of the many expansion options available. The computer is housed in a two-piece plastic case. The upper section is pivoted on two plastic studs making it “click-fit” and thus easily removable. A clear plastic cover may be slid down to cover the keyboard and display. I found it easier to remove the lid completely as even with the cover slid out of the way, access to the keyboard is severely limited; requiring an awkward vertical stabbing motion.

Figure001

Fig.1 System architecture of the Samson/Sym. Enough to satisfy most single boarders.

The Samson is supplied fully assembled with two comprehensive manuals and a programmer’s reference card included. The only extras required are a 5V 1.5A power supply, suitably protected against overload, and a cassette recorder for low-cost program and data storage.

A high quality, double sided printed circuit board holds all the components including a 28 key ‘spongy-plastic’ keypad and a 6 digit 7 segment display. Also included is a piezo-electric ‘bleeper’ similar to those used in digital alarm watches. This gives an audible response each time a key is pressed making use of the keyboard a much more certain operation. Of course, it is all under software control and yes, you can play tunes on it! The ‘debug’ function is achieved with a hardware connection and this key does not give an audible response. However, the reference manual includes details for connecting a LED indicator which would easily remedy this omission. Though designated on the functional block diagram as a ‘Hex’ display, the on-board LED display consists of six standard seven-segment units resulting in the usual ‘abbreviated’ representation of the alphanumeric character set. The red display is nonetheless quite bright and easy to read. Use of a small piece of Polaroid would make it even better. A red plastic filter was included with our unit.

Sockets are provided for the MOS integrated circuits. Make sure the chips are fully inserted before applying power. A nice feature is the provision of blank sockets on the board enabling the memory to be expanded up to 4K and extra input-output to be fitted by simply plugging extra chips into the appropriate sockets. Extra RAM and a port expansion and connector kit are available as part of the Samson system. The overall layout of the printed circuit board is clean and uncluttered and component and connector positions are clearly marked on the component side in white ink.

Figure002

Fig.2 The Sym/Samson keyboard layout.

The documentation supplied with the Samson deserves a special mention. As well as a reference card containing op-codes, system addresses, etc, two manuals are supplied. One features all the information that you will ever need to know about the processor’s instruction set while the other contains essential data for the hardware orientated enthusiast as well as complete data sheets on the major LSI chips. Both are produced on good quality white paper with a wealth of diagrams and useful hints. These are the kind of books that cost you a fiver each in the shops and they come as standard issue with the Samson computer.

Chips

The heart of the system is a 6502 microprocessor running at a 1MHz clock frequency. This will be familiar to computer buffs as the 6800 derived powerhouse used in the KIM, PET, Apple, Acorn and Tangerine systems. (I wonder why hard-headed manufacturers choose such fruity names!) There are two 6522 Versatile Interface Adaptors in the basic system which handle input-output. These also contain software programmable timers which can be configured in numerous ways. In short, as their name suggests, they are versatile – very! Provision is made on board for insertion of a third 6522 if you can think of a use for it that is not already provided for. The board fairly bristles with connectors. These are high quality double sided, gold plated pads and mating sockets are provided either with the basic unit or are available as part of an expansion kit. Also present is a 6532, RAM, I/O, timer array which offers many features comparable to those offered by the 6522. What makes the 6532 special is the inclusion on-chip of 128 bytes of random access memory. This is software write-protectable and is used by the monitor to store system vectors and as scratchpad memory.

Memory

As well as the RAM contained in the 6532, 1K of RAM is provided in the basic system in the form of two 2114 (1024 x 4) chips. One 4K ROM chip holds the ‘Supermon’ monitor and there are spare sockets for an 8K BASIC interpreter and a resident assembler-editor. Pairs of 2114 chips are available as the ‘Samson Static RAM memory’ enabling expansion of the on-board RAM in 1K blocks up to 4K.

Monitor

The ‘Supermon’ monitor is the largest I have come across in a single board computer… and it does not stop there. Expansion is possible through the use of eight undefined keys (USR 0 thru’ USR7). These normally return control to the monitor via a vector address written into system RAM. By changing this address to point to a user written routine you can expand the facilities offered by the monitor in any desired way. Excellent and extensive hardware is provided on the Samson board and this is well used by the monitor which supports the following input-output and storage media:-

  • TTY – selectable current loop
  • VDU – RS232 interface. Baud rate is automatically determined by the monitor at log on.
  • Paper tape – data is stored as pairs of ASCII characters.
  • Audio cassette – two formats are available. The low speed system is KIM compatible and operates at 8 bytes/sec. A high speed mode is also provided and runs at 185 bytes/sec. A simple program is included in the reference manual enabling the generation and use of SYNC tapes facilitating adjustment of the cassette recorder. One with both volume and tone controls is recommended.
  • Oscilloscope display – this enables a single line of text containing up to 32 characters to be displayed on a conventional ’scope which is all you need to supply. A suitable software driver is included in the reference manual and instructions are given for generating your own character set.

The extensive use of command vectors enables the Samson owner to direct input-output to any chosen device(s). Some examples of how to do this are given in the manual which also contains a complete and legible listing of the monitor. This facilitates the use of monitor routines in your own programs and is an aid to anyone learning to use machine code. Table 1 shows the monitor commands and their function.

KIM Compatibility

The Samson is designed to be generally upwards compatible with MOS-Technology’s single board KIM computer. In practice this means that some of the connectors are different; for example, the Samson uses a separate connector for the power supply, and some of the signals are absent or renamed. Though both machines use the same microprocessor, the 6502, they are not directly software compatible. Inconsistencies include timer addresses and a number of monitor routines. Those most likely to concern the prospective user are the keyboard and monitor sections which feature most strongly in pre-written KIM software; for example, in the ‘First Book of KIM’. It is possible to use programs from this source. However, you will have to provide some software links to the Samson system. These are best provided in the form of subroutines which can be called when required. Here’s a tip. Remember that you must call ‘ACCESS’ before you can even begin to think of getting at the LED display.

BASIC

For anyone who turns white and shivers at the first mention of machine code, those nice people at Samson (Synertek – why pretend?) have come up with an 8K BASIC Interpreter. Supplied in the form of two 4K ROMs, it only requires plugging in to the sockets provided and a couple of wire jumper changes to be up and running.

With BASIC installed, following power-on, a TTY is logged on from the Hex keyboard or a VDU is logged on by typing ‘Q’. The monitor responds with a prompt Now if J 0 (CR) is entered, BASIC responds by asking for the memory size to be used. Any value greater than 512 bytes may be entered. BASIC will use all contiguous memory from location 0200 (Hex) to the value specified. This enables space to be reserved for machine code routines. You will then be asked to specify terminal width which determines the output line width for PRINT statements only. There is a default value of 72 characters though any value between 1 and 255 may be used. BASIC will then type out the number of free bytes, Synertek’s banner and ‘OK’. The prompt character (.) is replaced by a flashing cursor if you are using the Samson terminal.

There is no space here for a full description of the BASIC. It seems to have everything you would expect from an 8K interpreter and includes commands enabling you to use machine code routines in your programs. A sixty-page manual contains a brief history of BASIC with notes on its implementation in the Samson system and some worked examples and details of common pitfalls. There is certainly nothing wrong with the BASIC provided and it is good to see it offered as part of what looks at first glance like a simple development kit. However, I cannot help feeling that, if you want to talk BASIC, you should just go out; buy a PET, put the Programmer’s Toolkit on it and talk to that. PET speak heap good BASIC!… and the screen editing and graphics capabilities are excellent for a black and white system. The Samson is a superb piece of hardware with excellent software support and it seems foolish to ignore all that just to talk pidgin English!

Samson In Orbit

The Samson Satellite consists of yet another Synertek product, the KTM-2, in another plastic case. This is a full-size keyboard mounted on a single PCB which also contains circuitry to drive a display monitor. There are two models differing primarily in the number of displayed characters per line. The 40 character version may be used with an ordinary television while the 80 character unit requires a video monitor. An RF modulator is not supplied with either unit and must be purchased separately. Power requirements are simply 5V at about 1 amp.

Samson-1_003

A typical screen dump showing the squashed display. The Hex pair on the right is the checksum.

The keyboard consists of 54 keys which enable the full ASCII set and 128 graphics characters to be generated. Graphics and alpha-numerics may be displayed simultaneously and the cursor may be software driven using absolute or relative addressing. There are two full-duplex serial communication ports enabling the Satellite to interface to a computer and printer simultaneously. Transmission rate is adjustable between 110 and 9600 baud. There are eight ranges selected by three switches. Other switch selectable functions include:

  • even, odd or no parity
  • interlaced or non-interlaced display (an interlaced display may appear to flicker on a screen with a short persistence phosphor.)
  • line truncate or wraparound
  • choice of 50Hz or 60Hz frame rate.

Almost everything in the Satellite responds to automatic control. The cursor may be moved, screen cleared, graphics selected or deselected and reverse video turned on or off: all under software control. You enable the auxiliary communications port with an ASCII control code too!

Samson-1_004

How characters are made up on an oscilloscope display.

Samson-1_005

What you get when you jump to BASIC.

As you will see from our photos, the Satellite’s character rows are very close. This was done primarily for the graphics characters to connect in a vertical direction but does result in a rather cramped display with an awkward aspect ratio. One or two extra scan lines may be added by re-configuring some jumpers on the PCB. Full details are given in the 40 page A4 size manual which includes all the technical data required and adds some hints for users operating Synertek BASIC.

Figure003

Fig. 3. The graphics set of the Satellite terminal.

The Satellite is a well produced unit offering many sophisticated features and makes a good companion to the Samson-1. In conclusion, the Synertek BASIC and Satellite terminal are good. The Samson (Sym-1) is very good indeed and deserves to find wide acceptance in this country. If this article has whetted your appetite, all you have to do now is come up with the cash, go out and get one!

Table 1. The Supermon command set.
Command Function
M Display-modify memory
R Display-modify user registers
G Restore user registers, resume execution from PC
V Display 8 bytes of data with their checksum
D Deposit data from keyboard to memory
C Calculate using Hex arithmetic, displacements etc.
B Block move in memory
Jump (0-7) loads PC with address from system RAM
SD Stores a double byte
F Fills block of memory with chosen byte
W Write protect user RAM in 1K blocks
E Adjusts monitor to receive input from RAM
51 Save cassette tape KIM format
52 Save cassette tape high-speed
L1 Load KIM format tape
L2 Load high-speed tape
SP Save paper tape
LP Load paper tape
CR Carriage return
+ Advance 8 bytes
Retreat 8 bytes also used as delimiter
> Advance one byte or register
< Retreat one byte
USR0-7 User defined keys
SHIFT Select upper case
RST Reset
DEBUG Hardware debug function
ON-OFF  
ASCII Next two keystrokes combined to form one ASCII character.

 

Program to make the bleeper bleep, alter value at 011C to change note pitch
  100 20 88 81 JSR SAVER
  103 A9 0D   LDA 0D
  105 20 A5 89 JSR CONFIG
LOOP 108 A9 08   LDA 8
  10A 8D 02 A4 STA PBDA
  10D 20 1B 01 JSR
  110 A9 06   LDA 6
  112 8D 02 A4 STA PBDA
  115 20 1B 01 JMP LOOP
  11B A0 50   LDY 50
  11D 88     DEY
  11E DO FD   BNE FD
  120 60     RTS

First published in Computing Today, June 1980

Micro-Professor MPF-I

Even if by pest control you mean programming robot mice, the MPF-I should fit the bill. John Dawson reviews.

MPF1

The Micro-Professor must be one of the machines offering the best value for money in single-board computers available in this country at present. For less than £90 you can acquire a Z-80-based computer with keyboard and display on one board, a powerful monitor program, space to wire additional circuits on the main card and as much expandability as you can handle.

Before I received the Micro-Professor for review I had read only one previous article in which the author moaned continually about the inappropriateness of teaching computing at machine-code level. He said that what the younger generation needed was a broad appreciation of computing based, where necessary, on the use of high-level languages and that machine code was irrelevant except to a very few systems engineers.

This black-box approach to computers and their application is adequate – so far as it goes. If the machine you use runs much faster than you need and if you have the resources to purchase all the modules that you need, and if you never need to stretch the high-level language you use, then all will be well. If, on the other hand, you want to explore, and if you want to use a computer for a new purpose, something beyond other people’s experience, then you must understand more about how the black box is constructed and how it functions. You may not use machine code in your new application, but you are more likely to be successful if you understand something of the highways and byways of microprocessors.

The construction of a program in machine code is strictly comparable to using an ordinary Microsoft Basic. Both languages have facilities for taking information into the computer, processing data using conditional jumps, calls to subroutines, comparison and mathematical operators, and displaying the results in a form that is intelligible to the user.

The Micro-Professor computer is 6.2in. wide, 8.8in. deep from front to back, and just under 0.75in. thick. A 2.25in. loudspeaker is mounted on the board with the diaphragm at the rear. There are 36 hard plastic keys on the keyboard and the keys travel about 2mm. when they are depressed. The keyboard appears to be well-made and is pleasant to use with adequate inter-key spacing.

Information display

Information is displayed on six 0.5in. seven segment Light Emitting Diode – LED – displays and the character set that can be achieved using seven segments is shown in figure 1. At the rear, right side of the board are two 3.5mm. jack sockets for connection to a cassette-tape recorder and a power-input socket.

Figure 1

MPF1Display

A 7805 IC regulator is fitted on a heatsink and the manual says that the input voltage may be between 7 and 24V. A 230V mains power supply unit – PSU – is provided with generous leads about 6ft. long, and this provides 9V DC at about 500 mA.

The PSU was supplied with a 13A plug already connected. The PSU became cool-to-warm when the machine ran for several hours in the course of the review while the 7805 regulator heatsink became too hot to touch. The manual states that this will happen and explains that it is not a matter for concern.

In front of the power regulator is a breadboard area that may be used to hand-wire your own circuits. There is room for approximately eight 16-pin ICs or a mixture of the wider 24-pin packages with some 14- or 16-pin ICs and discrete components. 5V and ground rails are distributed throughout the breadboard area with convenient holes for a smoothing capacitor.

The Z-80 Central Processor Unit – CPU – is located at the rear left side of the Micro-Professor board and there are three 24-pin sockets for the Erasable Programmable Read Only Memory – EPROM – containing the fundamental operating program – the monitor, the RAM supplied with the machine, and one socket that may be used for either additional RAM or another EPROM.

Like the Apple computer, a number of jumper connections are available on the board. These must be either cut, or connected to alter the configuration to suit each of the various chips that may be plugged into the spare socket.

Unlike many other cheap – and not so cheap – computers, there is no need to fiddle about trying to connect wires to odd pins of other components – the options on the Micro-Professor board have been well thought out.

An 8255 Programmable Peripheral Interface – PPI – chip is used to drive the LED display and the keyboard. Two sockets are provided for a Parallel Input/Output – PI/O – chip and a Counter Timer Circuit – CTC – IC. Finally, and very important they are too, there are two standard, properly-designed, sockets on the extreme left of the board that carry all the connections to the Z-80 CPU and the signal lines from the PI/O and CTC chips.

The connections to the Z-80 form a bus that will, in theory, allow you to expand the Micro-Professor computer to a full 64K, twin floppy-disc, business-orientated system.

If you want to expand the computer, however, you will have to increase the drive capacity of the Z-80 bus. The data and address lines are not buffered on the main board. System buffering is carried out on the EPROM programmer board.

The printed-circuit board is well made with gold-plated connections, a green solder-resist on both sides and the component locations, and values silk-screened on to the top surface.

Two versions of the Micro-Professor computer have been marketed in this country. The original computer – MPF-I – had a 2K monitor only and this was extended in the MPF-IB to include a 2K Tiny Basic. The MPF-IB is now the only version that is available and this costs £75 plus VAT. The 20 monitor commands represent a reasonably comprehensive set facilities for entering, running and correcting machine code programs. In addition to the ability to enter data into a particular memory address you may load the Z-80 registers, and the alternative register set, with starting to run a program.

The SBR and CBR commands Set and Clear a single break-point to allow you to stop a program at a specified address to examine the status of the Z-80 CPU. The Move command is intelligent in the sense that the monitor calculates for itself in which direction data should be moved to avoid corrupting the memory. Other monitors of my acquaintance are not so smart.

Relative jumps

The Delete and Insert commands will move the data in the memory down or up one byte. The delete command removes the data at the address for which the command was entered and the Insert command enters a no-operation instruction – 00 Hex – at the address from which the instruction was entered.

Relative jumps can be calculated using the Rela command. The monitor assumes that the current address is the start of the jump, unless you enter a different number, and then asks for the jump destination. The relative offset is calculated and inserted into the location following the jump instruction. If the jump is outside the range that the Z-80 can handle an error message is displayed. There is no consistent way of recovering from errors except to reset the computer; this is acceptable in the Micro-Professor as the Reset key does not destroy existing programs or data.

The tape Read and Write commands are easy to use and the method of setting the start and end addresses for the block you wish to save is consistent with other block commands in the monitor.

The level control for the tape recorder is excellent; there is either sufficient signal from the tape recorder or not enough. When the output level from the tape recorder is high enough, a Schmitt trigger in the computer operates and the input signal can be heard on the loudspeaker. When the volume is low, the trigger does not operate and there is no sound and no input to the computer memory.

Programs that you save on tape may have file names consisting of a number between 0 and 255, and the monitor will search through a tape until it finds the correct program. When to counter criticism about machine-code programming for young people. Well, it does that and it has two instructions that make it very for controlling the PIO and CTC chips.

Two variables are reserved to access the Z-80 ports and RAM locations:

LET M 3477 = 750

stores the value 750 at the decimal address 3477. The instruction works the other way in this form:

LET A3 = M 3991

which will get the value stored at RAM location 3991 decimal and store it in variable A3.

There are similar instructions for the P variable which relate to the Z-80 port addresses. The Micro-Professor instruction is only a convenient Deek and Doke alternative but the P instruction is an original and useful idea.

When you are programming in Basic the machine takes a single keystroke as the input for a whole instruction. The keywords are printed on to a template which slips over the original keyboard.

There are three manuals for the Micro-Professor computer and a fourth which describes the Tiny Basic. The Micro-Professor manuals total 300 pages of information about the hardware, the software, and a series of experiments and other programs. What is there left to say about Oriental English?

The Micro-Professor manuals are no worse than many others and it is usually possible to figure out what the author intended to say. They are unsuitable for a first-time user who needs the constant reassurance of accurate documentation if she or he is to cope with unfamiliar and complex concepts.

The monitor listing is a fully-commented source listing and it would be very easy to modify the monitor by changing bytes here and there before “blowing” it into another EPROM.

The listing takes 51 pages for 2K and most of the useful subroutines start with a description of the function of the routine, a note of the input that is required, the output in various conditions, which of the Z-80 registers are corrupted and which other subroutines are called. The monitor and its documentation is up to the standard of one of the original Intel evaluation kits – very good.

The Experiment Manual covers the software and hardware and includes a full description of the CTC chip and its use. The Japanese English is much less severe in this book and I think that large sections have been written for native English speakers. The Users’ Manual includes a full set of circuit diagrams for the computer and an adequate and reasonably well set-out explanation for each of the monitor commands.

One of the options for the Micro-Professor computer is an EPROM programmer board. The board is constructed to the same high standards as the main computer. A 40-way flat cable connects the EPROM board to the Micro-Professor and there is an extension socket on the second board to allow the Z-80 bus, now fully buffered, to be connected to additional equipment. The EPROM programmer will handle six types of EPROM and changes to the pin functions are made by the software – there are no “customising” plugs to lose. Clearly, once you have written and debugged your program, you can fix it in an EPROM and plug that into the spare socket on the main board. The programmer has a separate PSU for both the ordinary 5V supply and the 25V used for programming the EPROM chip.

Conclusions

  • The Micro-Professor hardware is excellent, provided you can manage with the single-location, six-character display.
  • The Z-80 CPU is a good microprocessor to program in machine code as the high-level instructions for
    Block Move and Compare operations, and the 16-bit register operations, allow more productive programming than the 6502.
  • The plug connecting the 5V supply to the board became intermittent a couple of times and I would want to replace that with something more solid. With that exception I have nothing but praise for the hardware.
  • Someone must be writing a Tiny Forth for the Micro-Professor. Rather than attempt to fit a limited and elementary Basic into the remaining space in the monitor I would like a series of useful subroutines – delays, PI/O control, printer interface, interrupt-driven timers working in the CTC, simple maths operators using RPN, and so on – which could be linked to form more complex modules within a user’s programs.
  • The Micro-Professor is both a serious tool and a lot of fun for anyone with an interest in low-level, real computing. I hope to buy a Micro-Professor and use it, battery-operated, on my commuter train.

First published in Your Computer magazine, December 1982