Hardware
| Catalogue ID | HW-0402 |
|---|---|
| Manufacturer | ORPHANWARE/C.L. DIGITAL |
| Region | United States |
| Person or team | John Lingrel/Ron Collins |
| Product number | P/N SI1A/B |
| Type | Serial Parallel Interface (Interface) |
| Connects via | External Expansion Bus |
| Platform | ADAM |
| Status | Released |
| Source | Collectors DB v1.00 Master |
RS-232 serial port expansion card for the Coleco ADAM, connecting via the side expansion port (60-pin card edge). Provides a standard RS-232 serial interface for modems, terminals, printers, and other serial peripherals. Housed in a white plastic enclosure with ribbon cable to the ADAM and pin header for the serial output cable.
Key ICs (verified from board photography — 7 ICs total):
SCN2651 (Signetics, 28-pin DIP) — Programmable Communication Interface (USART). The serial engine handling baud rate generation, character framing, parity, and transmit/receive buffering. Same chip family used 40 years later in MicroFox's 80-column VGA cards.
MC1488N (Signetics) — Quad RS-232 line driver. Converts TTL logic levels to RS-232 voltage levels (±12V) for the serial output.
DS1489N (TI) — Quad RS-232 line receiver. Converts incoming RS-232 signals back to TTL levels for the USART.
74LS138 — 3-to-8 line decoder for I/O port address decoding.
SN74LS21N (TI) — Dual 4-input AND gate for address decode qualification.
74LS32 (Fairchild) — Quad 2-input OR gate for control logic.
74LS04 — Hex inverter for signal conditioning.
Architecture: Clean 7-IC design. The 74LS138, 74LS21, 74LS32, and 74LS04 form the address decode and control logic mapping the SCN2651 USART to a Z80 I/O port range. The MC1488/DS1489 pair handles RS-232 level conversion. A crystal oscillator provides the USART baud rate reference clock. Single-sided PCB with bare copper traces — no solder mask or silkscreen beyond the part number etched in copper.