Z80 RETROCOMPUTER
Compact computer with Basic in ROM.
With original Z80 CPU!
Easy to build.
The Z80 retrocomputer building kit
Go back to the seventies and eighties of the last century and see for yourself how
computing was in these days.
With this affordable building kit you can build your own Z80 retrocomputer with original Z80
CPU. The supplied ROM is already programmed with the BASIC language so it will be
easy to program.
The computer has a 32K RAM memory and all signals from the CPU are available in the
edge of the PCB. In this way you can add your own circuit designs if needed.
The output of the computer is serial and you need a TTL to USB serial cable and the free
terminal program Tera-Term. See downloadsection for the software on the left side down
on our website www.budgetronics..eu . You also can use your own terminal program or
solution for displaying the computer output. In the download package you also find some
Basic example programs to load into your computer using a terminal program.
To make this a stand alone computer you can add the ASCII video terminal building
kit. In this way you add a VGA video output or composite video output and a PS/2
keyboard input. See menu Buidling kits in our website www,budgetronics.eu for
more details about this kit.
CONTENTS BUILDING KIT
In the building kit you will find the following parts:
1x PCB
5x IC sockets (2x 14 pins, 1x 40 pins, 1x 24 pins and 1x PLCC32)
1x Original Z80 CPU
1x 74LS32 IC
1x 74HCT04 IC
1x SMD RAM IC KM62256 or similar
1x ROM AT27C040 with programmed Basic
1x 68B50 IC Asynchronous Communications Interface Adapter (ACIA) for serial
communication.
3x resistor 2K7 (red, violet,red)
1x resistor 2k2 (red, red, red)
1x resistor 470 (yellow, violet, brown)
1x resistor 1K (brown, black, red)
1x resistor 3k3 (orange, orange, red)
1x resistor 1M (brown, black, green)
1x quartz 3.6864MHz
2x ceramic capacitor 22pF
6x ceramic capacitor 100nF (104)
1x 6 pins header
1x LED 3mm
1x pushbutton for reset
Building the kit
We begin soldering the SMD RAM KM62256. For those not familiar with soldering SMD
parts it is not difficult if you follow the explanation here.
Take care soldering the RAM in the right postion. The photo below shows how.
Place circle on circle
Put a little solder on one of the corner connections like shown on the photo below.
Heat the solder and slide the IC to the corner and heat the IC pin and solder. Line the IC
out with all the other connections on the PCB. Solder the opposite corner only if all the
pins are lined out correctly. After this it looks like the photo below.
If all is lined out you solder all the other pins with a little bit of solder. Always look with a
magniying glass if al the connections are well made and if they do not make unwanted
contact with other pins. After soldering the RAM IC it will look like the photo below (maybe
even better if you are really good at soldering :-) )
If this is done the remaining soldering of the kit will be very easy. The most difficult part is
done now.
Solder all the IC sockets and line them up with the PCB indicators. See red arrows.
Solder the PLCC32 socket and make sure you do this the right way! The PLCC socket
can be soldered the wrong way and the ROM IC will not work correctly Look very careful
to the red arrow.
The small square come at the left side up as seen in the photo.
Connect the 6 x 100nf (code 104 or 100nf) capacitors as indicated by the red arrows
below.
Connect the push button.
Solder the 8 resistors with the correct values in the right place. For the color codes see the
description of the building kit contents above.
Connect the quartz of 3.6864MHz and the two 2x 22pf capacitors. On the PCB you will see
7,3728 but this is only for Z80 CPU's which can operate on 8 Mhz. If you want to try this in
the future you can place a 7,3728 Mhz quartz and need to use 115200 Baud as a speed
for the serial connection instead of 57600 Baud.
Connect the LED in the right way.
Do not forget to cut all the wires at the back of the PCB.
Keep some of the cut off wires because you will need some later.
Connect the 6 pins header.
Put all 5 IC's in the right sockets
Take care that all the IC pins go straight into the sockets. Sometimes you have to bend the
pins a little bit so they fit the socket. You can do this by placing one side of the IC against a
hard surface and press so the pins will be aligned in a 90 degrees corner.
Also take care that you place the IC's in the right orientation in the sockets. Look at the
picture below. The red arrows show the side with the small notch. This notch is also visible
on the PCB.
The last part is the placement of PLCC ROM IC. Push this IC flat in the socket all way
down. Watch the right orientation.
The last solder work is placing 3 wire bridges on the PCB, NMI, WAIT and BUSREQ. You
can use the cut off wires for this.
Now the computer is finished and will look the same as in the picture below.
The 5 Volt connector is not connected here because normally the 5 Volts comes from the
TTL to USB cable on the 6 pins header. Only if you have another solution you can use the
5 volts connector but NEVER connect them both to 5 volts.In a case like that use only the
Tx, Rx, and if needed the RTS, connections on the header.
If you have a serial to USB cable as shown below then you have all the connections you
need. The black wire (GND or -) is situated on the left side. The RED wire is + 5 Volts.
Yellow is Rx here and orange is the Tx connection. So this is exactly the opposite of what
is indicated on the PCB but this is the right way to connect. You always have to connect
the Rx to the Tx and theTx to the Rx of the serial connector. So crosswise. The other
connections are just as indicated on the PCB.
If you connect the power the LED will light up.
But before you do this check the PCB to see if you soldered in all the parts, made no
solder mistakes and that all the parts are placed and orientated in the right way.
You always can choose another way to read out the serial data. We have only shown you
one possible way to do this but there are more solutions. Maybe you still own a real
terminal or have made another solution like the the ASCII video terminal building kit as
mentioned earlier. In this way you add a VGA video output or composite video output and
a PS/2 keyboard input to make this a stand alone computer you can add See menu
Buidling kits in our website www,budgetronics.eu for more details about this kit.. It is all up
to you.
STARUP AND TESTING
This desribes the connection with a TTL to USB connection using Teraterm. If you have
another solution you can use the same setup variables as mentioned in this description.
Start Teraterm.
A window opens. Choose font 14 for a bigger more readable font format..
Connect the serial to USB cable between a PC and the Z80 retrocomputer and check that
the LED is on as prove of power up.
Click OK and goto menu Setup/Serial port
Type in baud rate 57600, Data 8 bit, Parity none, Stop 1 bit en Flow control hardware.
ATTENTION! If you have a serial to USB cable with only 4 connections +5V, GND, Rx, Tx
and no RTS, you have to set flow control to NONE instead of hardware.
(If you want to try to run the Z80 CPU on 7,3728 Mhz the you have to replace the quartz
kristal and put the Baud rate to15200, Remeber this will not always work with every Z80
CPU because the supplied CPU is made for 4 mhz speed.)
If nothing appears in the Port: box the the Z80 computer is not connected to the PC or the
USB to serial interface is not recognized. Check this. Below you see COM3 but this can be
another COM port on your computer. As long as the PORT box shows a COM then there is
a connection. Click OK and the setup is done.
If all is right the word “disconnected” at the top of the Teraterm window disappeared. If this
is not the case go back to setup/serial port and press OK again.
Press the reset button on the Z80 computer and if all is welll you see:
If you get this message congratulations the computer works. If not go back check
everything and read this manual again to find the fault.
The computer asks for Warm or Cold start. Choose C. The Warm start is only needed if
there is a program in memory which you do not want deleted.
At the question memory top? Just press enter and you will see a startuo message that
You now can begin programming the computer with the following commando's:
SGN,INT,ABS,USR,FRE,INP,POS,SQR,RND,LOG,EXP,COS,SIN,TAN,ATN,PEEK,DEEK,L
EN,STR$,VAL,ASC,CHR$,LEFT$,RIGHT$,MID$
END,FOR,NEXT,DATA,INPUT,DIM,READ,LET,GOTO,RUN,IF,RESTORE,GOSUB,RETURN,R
EM,STOP,OUT,ON,NULL,WAIT,
DEF,POKE,DOKE,LINES,CLS,WIDTH,MONITOR,PRINT,CONT,LIST,CLEAR,NEW
TAB,TO,FN,SPC,THEN,NOT,STEP
+,-,*,/,^,AND,OR,>,<,=
Explenation about how to program Basic goedsto far for this manual. There are enough
books available about this subject.
To test the computers Basic type in the following program: (After each line press ENTER):
10 A=0
20 PRINT A
30 A=A+1
40 GOTO 20
Type in LIST to see if the program looks exactly the same as shown here. If so type in
RUN and the program will start and will count. To break out of the program pres Ctrl and C
together.
There is a small download package for this computer available on our website
www.budgetronics.eu. Not only the terminal program Teraterm is in this package but also a
nice collection of old Basic programs. Look on the left side, down, menu DOWNLOADS.
You can open the Basic listings with Notepad.
You can type in these listings but there is a faster way.
Open a progranm in Notepad:
1. Click in the Notepad page.
2. Hold Ctrl A to select the whoe text.
3. Hold down righthand mouse button and select copy.
4. Click with the right hand mouse button in Tera Term window and a window pops up
as shown below. Click on OK.
You will see the program is now transfered to the Z80 retrocomputer. After it finished you
can type in the LIST command to see if it was transfered correctly. If so you can give the
command RUN and you can play the game.
If you want the break in to the program press Ctrl C together and the computer will stop.
If you want to erase memory for another program just type in the command NEW.
It can happen that the program is not transfered correctly. This can happen when your
USB to serial connection is delayed for some reason or if you do not use Flow control in
the serial setup. This can be solved. In this case Goto menu Setup/serial port and change
0 in box “transmit delay” in say for example 10. You will see transfer is a lot slower but
correct.
You can change the programs if you want or write your own but if you remove power all will
be lost.
To preserve programs you can save them. In the Tera term window select the
programcode and click the right hand mouse button. A pop up appears with the selected
text inside. If you want you can paste the text in an empty Notepad page and save it.
This is the most simple method but you can also experiment with Tera Term menu
File/Transfer ,Xmodem, Ymodem, and so on, to send and receive. Try it out and
experiment to learn.
If you add the ASCII VT100 terminal building kit to this computer, just connect the RX to
the TX and the TX to the RX connection (crosswise) and also connect the GND
connections of both modules together, supply the Z80 computer and the ASCII video
module with 5 volts power, use the setup menu of the ASCII terminal to adjust the serial
setup to the right specs, as described above, and you are ready to go.
Have a lot of fun with the Z80 Retrocomputer!
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