Zx81-external ram
About the Zx81-external ram PCB
Zx81-external ram is an open source PCB design by zxinfo-diy-electronics, published on GitHub. It is a 2-layer board measuring 59.8 × 42.7 mm, with 15 components from 11 distinct parts.
Other key parts include the CY62256-70PC, 74LS00 and 74LS32. By type, the board carries 4 diodes, 4 capacitors, 3 ICs, 3 resistors and 1 connector.
It belongs with the retro computing designs in this gallery.
From the project
ZX81 External 16K/32K RAM interface with WRX hi-res support
The interface has been tested with the following 32K SRAM chips, all running Beamrider perfectly. - UM62256E-70LL - HM62256BLP-10 - AS6C62256-55PCN
- Cut the ROMCS trace on the back - and put in a diode, eg. 1N4148 instead - as shown here:
And now it runs fine with the zx81-external-eprom interface as well.
BOM for v1.2 (ROMCS fix) - same as v1.1 - Diode 1N4144 (or similar)
Main components on the Zx81-external ram
Zx81-external ram bill of materials (BOM)
15 components, 11 distinct parts.
| Qty | Part | Footprint | Refs |
|---|---|---|---|
| 1 | CY62256-70PC | DIP-28_W15.24mm | U1 |
| 1 | 74LS00 | DIP-14_W7.62mm | U2 |
| 1 | 74LS32 | DIP-14_W7.62mm | U3 |
| 1 | Connector ZX81 | EDGE ZX81 BOTTOM | J1 |
| 1 | LED | LED_D3.0mm | D1 |
| 3 | 1N4148 | D_DO-35_SOD27_P7.62mm_Horizontal | D2, D3, D4 |
| 3 | 100nF | C_Disc_D3.0mm_W1.6mm_P2.50mm | C1, C2, C3 |
| 1 | 1,2nF | C_Disc_D3.0mm_W1.6mm_P2.50mm | C4 |
| 1 | 470 | R_Axial_DIN0207_L6.3mm_D2.5mm_P10.16mm_Horizontal | R1 |
| 1 | 4K7 | R_Axial_DIN0207_L6.3mm_D2.5mm_P10.16mm_Horizontal | R2 |
| 1 | 10K | R_Axial_DIN0207_L6.3mm_D2.5mm_P10.16mm_Horizontal | R3 |
Zx81-external ram design files
The KiCad project lives in the zxinfo-diy-electronics/zx81-external-ram repository on GitHub; these links point at the commit this page was built from.
- Layoutzx81-external-16k.kicad_pcb
- Schematiczx81-external-16k.kicad_sch
Zx81-external ram: common questions
How big is the Zx81-external ram PCB?
The Zx81-external ram measures 59.8 × 42.7 mm, has 2 copper layers and is 1.6 mm thick.
How many components are on the Zx81-external ram?
15 components, from 11 distinct parts. The full bill of materials is listed on this page.
Where can I download the Zx81-external ram design files?
From the zxinfo-diy-electronics/zx81-external-ram repository on GitHub, which has the KiCad layout and the schematic; the links under Design files point to each one.
Can I use the Zx81-external ram design in my own project?
The repository has no license, so all rights stay with zxinfo-diy-electronics. Use it as a reference, and ask the author before reusing the design.
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