Summary of Contents for TK ZX81
- Page 1 ZX81 - 32KB internal RAM Build-up description 06.04.2018 Copyright History History History History History V1.0 06.04.2018 06.04.2018 Page 1 of 16...
- Page 2 (see ZX81 webpage: http://www.zx81.de/hardware/32k-ramd.htm) I‘ve taken this idea, because I‘d liked to enhance my own ZX81. So based on above page I build a small PCB board (without the backup battery buffer) that can be directly placed into your ZX81 after doing some solderwork.
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Page 3: Table Of Contents
Table of content GENERAL BUILD UP TIPS....................4 32KB INTERNAL RAM EXTENSION..................5 Short description ......................5 Component List (default) ....................7 32KB PCB component placement(s) in pictures ..............8 TIME TO DO SOME TESTING ................... 15 SCHEMATIC........................16 06.04.2018 Page 3 of 16... -
Page 4: General Build Up Tips
General build up tips As always when soldering electronic components, you should start with the smallest components, e.g. Resistor, Diodes first following next size components until all components are soldered. THIS IS TYPICALLY NOT DONE BY THE SUPPLIER OF YOUR PURCHASED PACKAGE. 06.04.2018 Page 4 of 16... -
Page 5: 32Kb Internal Ram Extension
When the ULA is forced to output the display-file to your screen, this is indicated to the ULA with the signal /M1 = LOW and A15 = HIGH. Because the display-file is located in the 16-32K area of your ZX81, A15 for the RAM must be LOW when /M1 = LOW. - Page 6 Having finished soldering the IC socket, fit some short wire at the place of LK2 (see above LK1/LK2 silk print at • the right side of IC4) That’s all for the first time when it comes to the ZX81 PCB board. Now let’s start assembling the new 32KB PCB board. 06.04.2018...
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Page 7: Component List (Default)
Lead (7cm length) - /M1 edge connector Pin A22 DIL socket, 28 pin, standard Soldered at ZX81 PCB position IC4 Jumper lead (1cm length) Soldered to ZX81 PCB Jumper LK2 06.04.2018 Page 7 of 16... -
Page 8: 32Kb Pcb Component Placement(S) In Pictures
32KB PCB component placement(s) in pictures Start soldering of the SMD part(s) – IC1 74LS00 • if you want to run HRG8, solder a SMD 0805 resistor of 10K ohms at position R1 06.04.2018 Page 8 of 16... - Page 9 now solder the 2 Pin Header, each 14 Pins, RM2,54 as shown above • 06.04.2018 Page 9 of 16...
- Page 10 place and solder IC2 – HM62256 SRAM PDIP • 06.04.2018 Page 10 of 16...
- Page 11 now add and solder the leads according the BOM (I used coloured leads as you can see) • 06.04.2018 Page 11 of 16...
- Page 12 PCB into the ZX81 IC4 socket • 06.04.2018 Page 12 of 16...
- Page 13 and to solder the leads according their written assignment to the corresponding diodes (cathode side) • 06.04.2018 Page 13 of 16...
- Page 14 A22 • I hope that everything went well and it’s now time to reassemble your ZX81. Take care about the keyboard flat cables and that they are not bend or damaged. Pause for a while… take some coffee/tea or some beer (depending on your choice) and start cleaning your workdesk.
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Page 15: Time To Do Some Testing
Time to do some testing Connect your ZX81 to your preferred screen and connect the power leads to start your ZX81. It now takes some time until the K cursor appears because the first 16k will be tested per default. -
Page 16: Schematic
Schematic 06.04.2018 Page 16 of 16...
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