IBM PC 5150
The first IBM PC: a 16-bit 8088 on an 8-bit bus, with beep codes and cassette BASIC as the first clues.
Open the IBM PC 5150 in Retro Bench- Also
- PC, Model 5150
- Year
- 1981
- CPU
- 8088 at 4.77 MHz (14.31818 MHz / 3). 16-bit core, 8-bit bus
- RAM
- 16 to 64 KB on the planar; more with expansion (verify)
- ROM
- BIOS 8 KB at $FE000 (U33). Cassette BASIC 32 KB at $F6000 (U29 to U32)
- Video
- MDA or CGA card in an expansion slot. The planar has no video
- Sound
- One-voice speaker, driven by timer 2 and PPI port B
- OS
- PC DOS 1.x (disk). Cassette BASIC in ROM if no disk boots
Chips
| Chip | Where | Role |
|---|---|---|
| 8088 microprocessor | U3 | CPU with a 16-bit core and an 8-bit external bus. Used in the IBM 5150, 5160, 5155, PCjr and the HERO 2000. |
| 8284A clock generator and driver | U11 | Crystal oscillator, divide-by-3 CPU clock, ready synchronizer and reset for the 8088. |
| 8288 bus controller | U6 | Makes the memory and I/O strobes and the bus direction for the 8088 in maximum mode. |
| 8259A programmable interrupt controller | U2 | Eight interrupt inputs (IRQ0 to IRQ7), priority logic and the vector for the 8088. |
| 8253-5 programmable interval timer | U34 | Three 16-bit counters: time-of-day tick, DRAM refresh pacing and the speaker tone. |
| 8255A-5 programmable peripheral interface | U36 | Three 8-bit programmable I/O ports (A, B, C). |
| 8237A-5 DMA controller | U35 | Four DMA channels. PC: channel 0 refreshes DRAM, channel 2 is the diskette. |
| 8087 numeric data processor | U4 | Optional floating-point coprocessor in the empty socket beside the 8088. |
| 4116 DRAM 16K x 1 | Planar RAM (designators not read) | Dynamic RAM, 16K x 1 (lower 16K on the Spectrum) |
| 2364 Mask ROM 8K×8 | U29-U32 cassette BASIC (5700019, 5700027, 5700035, 5700043) and U33 BIOS (5700051 on the photographed board) | BASIC and KERNAL ROMs (C64); BASIC and KERNAL (VIC-20, PET); character ROM (C128) |
| MC6845 CRT controller | MDA/CGA card (not the planar) | Makes sync, display enable, cursor and the video RAM refresh addresses. |
Ports and connectors
- Keyboard (DIN-5), 5-pin DIN socket (180 degree), rear of the system board
- Cassette (DIN-5), 5-pin DIN socket (180 degree), rear of the system board
- Power P8 and P9 (PSU to system board), Two 6-pin keyed plugs on a 12-pin male header
- Expansion slot (62-pin I/O channel), 62-contact card-edge socket, 5 slots (A1-A31, B1-B31)
- MDA video (DE-9), 9-pin D-shell female on the Monochrome Display and Printer Adapter
- CGA video (DE-9, RGBI), 9-pin D-shell female on the Color/Graphics Monitor Adapter
- CGA composite (RCA), RCA phono jack on the Color/Graphics Monitor Adapter
- Parallel printer (DB-25), 25-pin D-shell female on the Printer Adapter or the MDA card
- Serial RS-232 (DB-25), 25-pin D-shell male on the Asynchronous Communications Adapter
- Game (DA-15), 15-pin D-shell female on the Game Control Adapter
Power rails
| Rail | Expect | Measure at |
|---|---|---|
| +5 V | 4.80 to 5.25 V (+5 / -4 percent) | pc-psu pins P9-4, P9-5, P9-6; 8088 pin 40 |
| +12 V | 11.52 to 12.60 V (+5 / -4 percent) | pc-psu pin P8-3; I/O channel B9 |
| -12 V | -10.92 to -13.20 V (+10 / -9 percent) | pc-psu pin P8-4; I/O channel B7 |
| -5 V | -4.60 to -5.50 V (+10 / -8 percent) | pc-psu pin P9-3; I/O channel B5 |
| Power Good | 0 to 0.4 V at switch-on, then 2.4 to 5.5 V at least 100 ms later | pc-psu pin P8-1; 8284A pin 11 |
Symptoms
- No beep, no picture: check 8088, 8284A, 8288
- No Power Good
- One long, one short beep: check 8259A, 8253
- One long, two short beeps: check 6845
- One long, three short beeps
- Continuous tone
- Never-ending series of long beeps: check 8255A
- Repeating short beeps: check 8237A
- 201 (RAM error): check 4116
- PARITY CHECK 1: check 4116
- PARITY CHECK 2: check 4116
- 301 (keyboard error): check 8255A
- Dead keyboard: check 8255A
- 601 (floppy error): check 8237A
- 131 (cassette loopback)
- Cassette BASIC appears
- 161, 162, 164