How to build your own micro UK101
(serial only - no keyboard/display)
...on-line since 1998 !
(You can also create a complete UK101 (with display etc.) on FPGA - click HERE)
by Grant Searle
For news and updates, follow me on Twitter:Last update: 2nd January 2014
Please
note that you are NOT allowed to reproduce any of this page elsewhere on
the Web without my permission.
Introduction
Memory Map
Circuit Diagram
Construction
Parts List
Wiring diagrams
ROM images
Pictures of the finished UK101
Using the micro UK101
Loading and saving
Picture of the original UK101
Links to some of my other pages
The micro UK101 described here is effectively the stripped-down "core" of the original UK101, and is no way intended to be the full UK101 implementation. I have removed the display and the keyboard circuitry and, instead, used a terminal emulation program (eg HyperTerm for Windows) as the keyboard/display. This has resulted in a very simple circuit which is suitable for use embedded-control applications as well as a fully-functioning computer. I have tried to make as few functional changes as possible to allow old software to work, wherever possible. As a result the BASIC ROM is totally untouched.
Although not the very simplest that can be designed, it is
still straightforward. It is slightly more complicated due to the following:
1. The CPU is to run at 1MHz to match the original UK101. As a result, suitable
clock division was needed to allow suitable serial speeds to be produced.
2. The ROM enabling in the original UK101 is not contiguous (in one block). This
circuit is designed to use the original software on the UK101 (patched as
needed) so the ROM needed to be enabled at two separate places in the memory
map. The ACIA and RAM also needed suitable address decoding.
Some patches have been applied to the CEGMON ROM to
ensure ALL I/O is via the serial port only, not to the screen.
The differences are illustrated in the table below:
| Original UK101 | The MicroUK101 |
| 3K RAM, expandable on-board to 8K | 32K RAM |
| 300 baud serial/cassette interface | 19200 baud serial interface. No cassette port needed as the PC can store the prorgams. |
| 16x32 display | All display via the terminal on the PC |
| TV output and serial I/O | Only serial I/O |
| 1MHz 6502 CPU | 1MHz (although up to 8MHz CPU clock speed is possible) |
| Keyboard input (32 keys soldered directly onto the board) | Input via serial connection |
| 12 inch x 15 inch board | 3 inch x 3 inch board |
| 1.5A supply current | 200mA supply current, probably less if CMOS CPU used. |
| Open-board construction (uncased) | Up to you! |
| Microsoft BASIC | Microsoft BASIC |
| Various monitors were available; CEGMON being a popular choice | CEGMON monitor. Patched to ensure all I/O is via the serial port only. |
This is an ideal project for anyone wanting to build their
first computer as there aren't many components and it can be
built using wire-wrap or on a breadboard (as I originally did
with this circuit) in a couple of evenings.
You will, however, need to blow your own EPROM image. A logic
probe or an oscilloscope will probably be a distinct advantage in
case it doesn't work.
The aim of this design is to match the ORIGINAL UK101 address space, so resulted in slightly more complicated decoding logic than would be needed for a contiguous ROM space.
0000-7FFF - RAM
8000-9FFF - Free space
A000-BFFF - BASIC ROM
C000-EFFF - Free space
F000-F7FF - ACIA
F800-FFFF - MONITOR ROM
Here is the complete circuit of the micro UK101.
The circuit is slightly more complicated than a fresh design due to the clock
requirements for the CPU and serial interface, and also the memory map that was
needed for the RAM, ROM and ACIA (see above).
Some notes on the circuit...
The CPU clock is 1MHz to match the original UK101. The
serial clock then needed to use this.
The 19200 baud interface clock is derived as follows.
The 74LS74 divides the 4MHz clock by 2 then the 2nd stage divides by 2 again for the
1MHz CPU clock.
The 74LS163 runs from 0000 to 1100 (13 cycles) then is reset to 0000 on next
clock (synchronous reset), because Qc and Qd is set to one, so divides the
4MHz clock by 13.
So, 4000000/13=307692 (approx)
The 6850 is set for div 16, so the final baud rate = 307692/16=19231 (approx)
which is close enough to the required 19200.
Different crystal frequencies can be used, and if a suitable one is chosen that also produces the appropriate serial clock with simpler division then the circuit would be simplified.
Clock doubling: I have tried with success, doubling the clock frequency of the 6502. To do this, Phi in would connect to the 2MHz connection on the 74LS74 instead of the 1MHz connection.
Construction could be done in many ways, including the
following:
Assuming you are going to follow my layout, please see the wiring diagrams section for full details of
the component layout and the point-to-point wiring needed.
My version was built on a 3 inch square piece of tri-pad
Veroboard (ie. the copper tracks on the reverse have breaks
regularly resulting in groups of three holes being connected
together. See the reverse view for further
details). I used wire-wrap wire which requires soldering but,
instead of wire wrapping, I used it for point-to-point wiring
instead. All components are soldered in first then the wire laid
across the soldered joint and heated with the soldering iron
until the insulation melts completing the joint. Using this wire
for point-to-point wiring is very quick and the whole board was
soldered-up this way in a few hours.
Begin construction by positioning the IC sockets (see my pictures below for guidance). Next I recommend wiring the data and address. As each wire is soldered it, mark it off on the wiring diagram. This helps avoid any errors resulting from missing connections.
Wire the glue-logic wiring next, again marking each connection on the wiring diagram as you proceed.
Finally, wire up the power supply connections to all of the chips. For clarity, these are not shown on the wiring diagrams.
Once all components are soldered and without any ICs inserted
into the sockets, connect a continuity tester between the power
supply pins. If a short exists then check the underside of the
board for any solder bridges. If all is well connect a power
supply (current regulated to 500mA if possible). Check the +5V
and 0V connections on each IC socket. Turn off the supply and
insert the ICs. Turn on the power supply. If the circuit is
working then expect a power consumption of around 210mA. Connect
to a computer running a terminal emulation program set at 19200
baud, 8 bit, no parity, 1 stop bit, no handshake. Press the Reset
button. If you see the microUK101 prompt then well done!
This is a full list of discrete components required to build the UK101 excluding any hardware such as power supplies, nuts and bolts etc.
Component Type Qty No IC1 6502 1 IC2 62256 1 IC3 27256 1 IC4 MAX232* 1 IC5 6850 1 IC6 74LS04 1 IC7 74LS163 1 IC8 74LS74 1 IC9 74LS138 1 IC10 74LS00 1 IC11 74LS02 1 X1 4MHz crystal 1 C1-C5 1uF to 22uF 16V* 5 C6 470pF 1 R1 4k7 1 R2,R3 680R 2 Optional 0.1uF (decoupling) 2-3
* A MAX202 could be used instead, in which case C1-C5 should be 0.1uF Other Tri-pad Veroboard WireWrap wire 14 pin DIL socket 4 16 pin DIL socket 3 24 pin DIL socket 1 28 pin DIL socket 2 40 pin DIL socket 1 Connectors for power and serial I/O
Back to contents
Layout
Component layout of the prototype is as shown below. Please note the positioning of the components in relation to the tri-pad tracks.
Wiring
The following diagrams show the data, address and signal
connections. I have not shown the power connections, for clarity, but ensure
that the appropriate pins of every IC are connected to Vcc (+5V) and Gnd (0V) as
needed.
Wiring required for the data and address buses
The A0...A14 and D0...D7 on each chip are connected to the corresponding pin on other chips as identified below...
Wiring of the decoding, clock and serial interface
The remaining connections are shown here.
Power connections
Ensure all Vcc and Vpp pins are connected to +5V and all Vss/Gnd
pins are connected to 0V.
Additionally, I would recommend adding a couple of 0.1uF capacitors at various
points between the two power rails. I have found that this decoupling has not
been necessary, but it is recommended.
The full ROM here is 32K long. Only part of it is actually used and all gaps are filed with FF which means that most EPROM programmers will skip these unused parts very quickly.
Click here to download (zip file)
This ROM consists of BASIC occupying the first 8K and CEGMON occupying the last 2K.
The original BASIC is untouched - it is identical to the original found in my UK101.
The original CEGMON ROM has been patched to allow it to work without needing a dedicated keyboard/screen. Details of the patches applied are shown here.
PICTURES OF MY EARLIER PROTOTYPE VERSION
A scan of the original CEGMON manual is available here. Please note that the commands relating to text positioning or windows are not applicable as this version is a pure serial interface.
BASIC usage
Connect the microUK101 to a terminal running at 19200 baud, 8
bit, no parity, no handshake.
Ensure CAPS-LOCK is ON on the terminal. Press RESET on the
board and the following message will appear:
Micro UK101 C/W/M?
Press "C". The following message will appear:
MEMORY SIZE?
Press ENTER to allow the full memory to be used by BASIC. After a few seconds the following message will appear:
TERMINAL WIDTH?
Press ENTER. The following messages will be displayed:
31999 BYTES FREE
C O M P U K I T U K 1 0 1
Personal Computer
8K Basic Copyright1979
OK
The computer is now ready for programming in BASIC!
Back to contents
Save
Type LIST but don't press enter.
In your terminal window on the PC, or whatever you are using to operate this
board, enable the capture to the text file.
Press ENTER.
The listing will then be spooled to the text file on your PC.
Once the listing is complete, end the capture. The contents of the program will
then be on the PC for later use.
Load
Most terminal programs have a method to pass a text file to the destination.
Ensure the microUK101 is ready to receive characters and then transfer the text
file from the PC to the microUK101 using the terminal.
When transferring, you MUST have a delay after each new line, otherwise the
BASIC interpreter will not be ready to accept the next line, so characters will
be lost. You may possibly need a small delay after each character sent as well. This can be done in "HyperTerm" (for Windows) and may be available in
other terminal emulators.
LINKS TO SOME OF MY OTHER PAGES
Build your
own ZX80 - my page showing
you how to build this old micro
|__
ZX80 to
ZX81 conversion - build the NMI generator needed to convert the ZX80 circuit
into a ZX81
|__
ZX80
software - Type in a Space Invaders game into the ZX80
Build your own Jupiter Ace - my page showing
you how to build this old micro
Build your own UK101 - my page showing you how to build
a greatly simplified version of this old micro
Pong - Pictures of
my build of the Atari classic arcade game
My
Machines - My collection of classic 80's micros
I hope this page has been useful.
Grant.
To contact me, my current eMail address can be found here. Please note that this address may change to avoid spam.
Note: All information shown here is supplied "as is" with no warranty whatsoever, however, please let me know if there are any errors. All copyrights recognised.
