MSX1 (generic)
One standard, many makers: the same chips, ports and BIOS on very different boards.
Open the MSX1 (generic) in Retro Bench- Also
- Any MSX1 machine (Sony HitBit, Philips VG, Yamaha CX, Toshiba HX, Canon V, Sanyo MPC and others)
- Year
- 1983
- CPU
- Z80A @ 3.579545 MHz (one wait state in each M1 cycle)
- RAM
- 8 KB to 64 KB (BASIC uses at most 32 KB, $8000-$FFFF)
- ROM
- 32 KB MSX-BASIC 1.0 + BIOS in slot 0
- Video
- TMS9918A (NTSC) or TMS9929A (PAL) with 16 KB VRAM: 256 x 192, 16 colors, 32 sprites
- Sound
- AY-3-8910 PSG, 3 voices + noise at 1.79 MHz; 1-bit key click from the 8255
- OS
- MSX-BASIC 1.0 (MSX-DOS with a disk interface)
Chips
| Chip | Where | Role |
|---|---|---|
| TMS9918A / TMS9928A / TMS9929A video display processor | Varies by maker; TMS9918A (NTSC) or TMS9929A (PAL, also TMS9928A); 40-pin DIP beside the VRAM | Video display processor (VDP) with its own 16 KB DRAM bus. Composite out on 9918A; Y, R-Y, B-Y on 9928A/9929A. |
| Z80A CPU | Varies by maker; Z80A or a second source | Main CPU (8-bit, 40-DIP) |
| AY-3-8910 programmable sound generator (40-pin) | Varies by maker; AY-3-8910 or Yamaha YM2149, or inside an MSX-Engine on late boards | Three tone voices, noise and envelope, plus two 8-bit I/O ports (the MSX joystick ports and the cassette input) |
| 8255A-5 programmable peripheral interface | Varies by maker; 8255 at I/O $A8-$AB (or inside an MSX-Engine on late boards) | Three 8-bit programmable I/O ports (A, B, C). |
| 23256 mask ROM 32K x 8 | Varies by maker; the 32 KB BIOS / BASIC ROM in slot 0 (the chip-select pins differ between makers: check against the board) | 32K x 8 mask ROM in the 27256 pinout. |
| 4116 DRAM 16K x 1 | VRAM on boards with eight 16K x 1 parts (needs +12 V and -5 V); other boards use 16K x 4 parts | Dynamic RAM, 16K x 1 (lower 16K on the Spectrum) |
| 4164 DRAM 64K×1 | Main RAM on 64 KB machines (eight 64K x 1) | Main RAM (8 chips = 64 KB) |
Ports and connectors
- Cartridge slot, 50-way 2.54 mm card-edge socket (25 + 25), odd pins one side, even the other UNVERIFIED
- General-purpose I/O port 1 (joystick 1), DE-9 male on the computer ("9-pin AMP compatible")
- General-purpose I/O port 2 (joystick 2), DE-9 male on the computer ("9-pin AMP compatible")
- Cassette interface, 8-pin DIN 270 degrees (DIN 45326)
- Printer port, 14-pin Amphenol (Centronics-style ribbon) connector
- Video / audio DIN (where fitted), 5-pin DIN 180 degrees
- Composite video (RCA, where fitted), RCA (phono) jack
- RF out (to the TV aerial input), RCA (phono) jack
- Audio out (RCA, where fitted), RCA (phono) jack
Power rails
| Rail | Expect | Measure at |
|---|---|---|
| +5 V | +5 V | Z80A pin 11; TMS9918A pin 33; AY-3-8910 pin 40; 8255A pin 26; msx1-cart pins 45, 47 (cartridge) |
| +12 V | +12 V | Cartridge slot pin 48 |
| -12 V | -12 V | Cartridge slot pin 50 |
| -5 V | -5 V UNVERIFIED | 4116 pin 1 |
| GND | 0 V | Z80A pin 29; TMS9918A pin 12; AY-3-8910 pin 1; 8255A pin 7; msx1-cart pins 41, 43 (cartridge) |
Symptoms
- Power LED on, black screen, no boot beep: check Z80A, 23256, TMS9918A, 8255A, 4164
- Boots (beep, cartridge runs blind) but no picture: check TMS9918A
- Screen full of garbage, wrong characters or flickering blocks: check 4116, TMS9918A
- Several keys in one row or column dead, or ghost keys: check 8255A
- No RAM (tiny free memory) or cartridge ignored: check 8255A, 4164
- No sound, joysticks dead and tape will not load: check AY-3-8910
- Hum bars, resets when a cartridge or drive is plugged in, or dies after warming up
- Tape will not load: check AY-3-8910, 8255A