CPC Eightrom Card
This project is a ROM expansion board for the Amstrad CPC computers which is built entirely from 74 Series logic - no CPLDs or GALs or PALs to program here.
Although only 4 sockets are provided each can be filled with a 'double size' ROM to provide the equivalent of 8 classic 16KByte Amstrad ROMs.
The board will co-exist with other ROM cards and uses DIP switches to enable or disable ROMs individually and to select how the ROMs on the card will be numbered to avoid clashes with other cards.
Each ROM socket can take
- a 2764 8K EPROM
- a 27128 16K EPROM (the classic AMSTRAD ROM size)
- a 28C256 32K EEPROM
- a 27256 32K EPROM
- a 27C256 32K OTP EPROM
- a 27SF256 32K flash programmable EEPROM
These chips can be used in any combination.
NB When using 27SF256 parts, the 'EPROM' type should be selected rather than 'EEPROM' (see ROM Type Selection below). Although these parts are technically EEPROMS, they are designed to be fully pin compatible replacements for the older 27256 series EPROMs.
ROM selection is controlled by the 8 switches of DIP A (marked on the board).
| DIP Switch | ON |
|---|---|
| 1 | enable lower ROM SKT01 |
| 2 | enable upper ROM SKT01 |
| 3 | enable lower ROM SKT23 |
| 4 | enable upper ROM SKT23 |
| 5 | enable lower ROM SKT45 |
| 6 | enable upper ROM SKT45 |
| 7 | enable lower ROM SKT67 |
| 8 | enable upper ROM SKT67 |
When using a 2764 or 27128 on any socket, the ROM selection switch (see below) can be set to select either the upper or lower ROM for that socket, but not both.
The second set of 4 DIP switches (DIP B) controls the type of ROM in each socket
| DIP Switch | Closed | Open | Socket |
|---|---|---|---|
| 1 | EPROM | EEPROM | Skt01 |
| 2 | EPROM | EEPROM | Skt23 |
| 3 | EPROM | EEPROM | Skt45 |
| 4 | EPROM | EEPROM | Skt67 |
Finally, slightly below DIP B is a three pin jumper to select the ROM bank to be used.
- With the jumper closed in the upper position, the ROMs will be assigned to the logical slots 8-15.
- With the jumper closed in the lower position, the ROMs will be assigned to the logical slots 0-7.
Note that the CPC BASIC ROM occupies slot 0 on the motherboard, so this slot should normally be left open.
Also, if using the board with a CPC6128 or any machine with a DDI1 or other disk controller, then AMSDOS reserves the use of slot 7.
There are no restrictions on use of slots 8-15.
All programs and data files in this project are made available under the terms of the GNU General Public License v3.
All components are placed on the top side of the board according to the picture below.
I recommend HCT (or A(H)CT) logic for these cards, as shown in the tables and BOM above, since they are fast enough and draw less power compared with the older LS TTL series. Of course it's perfectly ok to build the entire board with LS chips instead.
It's possible to mix HCT and HC logic in the boards too. The HC parts do not have TTL compatible input stages, so generally shouldn't be used when driven by any LS TTL stages. The table below shows how HCT and HC can be mixed reliably for this board.
| IC identifier | Component | HCT | HC |
|---|---|---|---|
| U0 | 74HCT573 | ✅ | 🟥 |
| U1 | 74HCT138 | ✅ | 🟥 |
| U2 | 74HCT08 | ✅ | ✅ |
| U3 | 74HCT30 | ✅ | ✅ |
| U4 | 74HCT4075 | ✅ | 🟥 |
| U5 | 74HCT86 | ✅ | ✅ |
Below is a sample bill of materials with part numbers from Digi-Key.
| Manufacturer Part Number | Manufacturer | Digi-Key Part Number | Customer Reference | Reference Designator | Quantity | Unit Price | Extended Price | Description |
|---|---|---|---|---|---|---|---|---|
| EEA-GA1E220H | Panasonic Electronic Components | P15803CT-ND | Board decoupling | CAP22UF | 1 | 0.18000 | £0.18 | CAP ALUM 22UF 20% 25V RADIAL |
| 30350-5002HB | 3M | 3M157291-ND | MX4 Connector | CONN1 | 1 | 0.85000 | £0.85 | CONN HEADER R/A 50POS 2.54MM |
| DILB14P-223TLF | Amphenol ICC (FCI) | 609-4712-ND | 14 pin socket | U2,3,4,5 | 4 | 0.21000 | £0.84 | CONN IC DIP SOCKET 14POS TIN |
| DILB16P-223TLF | Amphenol ICC (FCI) | 609-4713-ND | 16 pin socket | U1 | 1 | 0.23000 | £0.23 | CONN IC DIP SOCKET 16POS TIN |
| DILB20P-223TLF | Amphenol ICC (FCI) | 609-4714-ND | 20 pin socket | U0 | 1 | 0.29000 | £0.29 | CONN IC DIP SOCKET 20POS TIN |
| B32529C1104J289 | EPCOS - TDK Electronics | 495-2479-1-ND | decoupling caps | CAP100N_1-8 | 8 | 0.25000 | £2.00 | CAP FILM 0.1UF 5% 100VDC RADIAL |
| DILB28P-223TLF | Amphenol ICC (FCI) | 609-4715-ND | 32 Pin socket | ROM01,23,45,67 | 4 | 0.34000 | £1.36 | CONN IC DIP SOCKET 28POS TIN |
| 1N4148TR | ON Semiconductor | 1N4148FSCT-ND | Diode | D0 | 1 | 0.08000 | £0.08 | DIODE GEN PURP 100V 200MA DO35 |
| QPC02SXGN-RC | Sullins Connector Solutions | S9337-ND | Jumper header | Bank | 1 | 0.08000 | £0.08 | "CONN JUMPER SHORTING .100"" GOLD" |
| PRPC040SAAN-RC | Sullins Connector Solutions | S1011EC-40-ND | PCB Pins | Bank | 1 | 0.51000 | £0.51 | CONN HEADER VERT 40POS 2.54MM |
| 206-4 | CTS Electrocomponents | CT2064-ND | DIP Switch 4 way | DIP B | 1 | 0.62000 | £0.62 | SWITCH SLIDE DIP SPST 50MA 24V |
| 4605X-101-103LF | Bourns Inc. | 4605X-101-103LF-ND | 10K SIL 5 pin | SIL1 | 1 | 0.38000 | £0.38 | RES ARRAY 4 RES 10K OHM 5SIP |
| 4609X-101-103LF | Bourns Inc. | 4609X-101-103LF-ND | 10K SIL 9 pin | SIL0 | 1 | 0.38000 | £0.38 | RES ARRAY 8 RES 10K OHM 9SIP |
| 206-8ST | CTS Electrocomponents | CT2068ST-ND | DIP Switch 8 way | DIP A | 1 | 0.81000 | £0.81 | SWITCH SLIDE DIP SPST 50MA 24V |
| SN74HCT573N | Texas Instruments | 296-1621-5-ND | Octal latch | U0 | 1 | 0.42000 | £0.42 | IC OCT D TRANSP LATCH 20-DIP |
| SN74HCT08N | Texas Instruments | 296-1606-5-ND | Quad 2 i/p AND | U2 | 1 | 0.36000 | £0.36 | IC GATE AND 4CH 2-INP 14DIP |
| SN74HCT138N | Texas Instruments | 296-1608-5-ND | 3:8 decoder | U1 | 1 | 0.47000 | £0.47 | IC 3-8 LINE DECODER/DEMUX 16-DIP |
| CD74HCT30E | Texas Instruments | 296-2111-5-ND | NAND 8i/p | U3 | 1 | 0.31000 | £0.31 | IC GATE NAND 1CH 8-INP 14DIP |
| CD74HCT4075E | Texas Instruments | 296-2157-5-ND | Triple 3 i/p OR | U4 | 1 | 0.69000 | £0.69 | IC GATE OR 3CH 3-INP 14DIP |
| CD74HCT86E | Texas Instruments | 296-2133-5-ND | Qual 2 i/p XOR | U5 | 1 | 0.52000 | £0.52 | IC GATE XOR 4CH 2-INP 14DIP |
