Pinout diagram
Summary specifications
Full pin reference
| Pin | Name | Group | Direction | Levels | Description |
|---|---|---|---|---|---|
| 1 | CAP1A | Analog | Bidirectional | Analogue filter cap | Filter capacitor C1, terminal A. The 8580 wants 22 nF here, not the 6581 470 pF. Connects across pins 1 and 2. |
| 2 | CAP1B | Analog | Bidirectional | Analogue filter cap | Filter capacitor C1, terminal B. 22 nF for the 8580; swapping the chip without swapping the caps gives a filter that sounds too open. |
| 3 | CAP2A | Analog | Bidirectional | Analogue filter cap | Filter capacitor C2, terminal A. Connects across pins 3 and 4. |
| 4 | CAP2B | Analog | Bidirectional | Analogue filter cap | Filter capacitor C2, terminal B. Match C1 and C2 for a tracked filter. |
| 5 | /RES | Control | Input | TTL, active low | Active low. Reset. Held low for at least 10 Phi 2 cycles to clear all registers and silence the output. |
| 6 | PHI2 | Clock / Timing | Input | TTL clock | Phi 2 system clock. All bus access is timed to this clock; data is valid only when Phi 2 is high. |
| 7 | R/W | Control | Input | TTL | Read / Write. High reads a register, low writes one. |
| 8 | /CS | Control | Input | TTL, active low | Active low. Chip select. Low enables the data bus; high tri-states D0 to D7. |
| 9 | A0 | Address Bus | Input | TTL | Register select bit 0. |
| 10 | A1 | Address Bus | Input | TTL | Register select bit 1. |
| 11 | A2 | Address Bus | Input | TTL | Register select bit 2. |
| 12 | A3 | Address Bus | Input | TTL | Register select bit 3. |
| 13 | A4 | Address Bus | Input | TTL | Register select bit 4. A0 to A4 select one of 32 register addresses. |
| 14 | GND | Ground | Power | 0 V | Ground. Run separately to the supply to keep digital noise off the analogue stages. |
| 15 | D0 | Data Bus | Bidirectional | TTL, 0 V / 5 V | Data bus bit 0. |
| 16 | D1 | Data Bus | Bidirectional | TTL, 0 V / 5 V | Data bus bit 1. |
| 17 | D2 | Data Bus | Bidirectional | TTL, 0 V / 5 V | Data bus bit 2. |
| 18 | D3 | Data Bus | Bidirectional | TTL, 0 V / 5 V | Data bus bit 3. |
| 19 | D4 | Data Bus | Bidirectional | TTL, 0 V / 5 V | Data bus bit 4. |
| 20 | D5 | Data Bus | Bidirectional | TTL, 0 V / 5 V | Data bus bit 5. |
| 21 | D6 | Data Bus | Bidirectional | TTL, 0 V / 5 V | Data bus bit 6. |
| 22 | D7 | Data Bus | Bidirectional | TTL, 0 V / 5 V | Data bus bit 7. |
| 23 | POTY | Analog | Input | Analogue paddle | Paddle Y input. An RC charge time on this pin is digitised to read a potentiometer. |
| 24 | POTX | Analog | Input | Analogue paddle | Paddle X input. Same RC ADC as POTY for the second axis. |
| 25 | VCC | Power | Power | +5 V | Logic supply. Decouple with 100 nF close to the pin. Separate from the analogue supply on pin 28. |
| 26 | EXT IN | Analog | Input | Analogue, max 0.6 V | External audio input. Mixed with the internal voices before the filter; keep below 0.6 V. |
| 27 | AUDIO OUT | Analog | Output | Analogue, rides at half VDD | Audio output. AC-couple with 1 to 10 uF. Check its DC bias — roughly half the pin 28 supply — before blaming the chip; a shorted output coupling capacitor mimics a dead SID. |
| 28 | VDD | Power | Power | +9 V | Analogue supply. +9 V on the 8580, NOT +12 V as on the 6581. Fitting an 8580 into a 6581 socket without dropping pin 28 to 9 V will eventually kill it. Adapter boards that regulate 12 V down to 9 V exist for exactly this. |
Common uses and repair diagnostics
The MOS 8580 is the later version of the SID sound chip, found in the C64C and the C128D. It is pin-for-pin identical to the 6581 EXCEPT for the voltage on pin 28: +12 V on the 6581, +9 V on the 8580. Fitting an 8580 into a 6581 socket without dropping pin 28 to 9 V will eventually kill it. The filter capacitors differ too: the 6581 wants 470 pF, the 8580 wants 22 nF. Swap the chip without swapping the caps and the filter sounds wrong.
The 8580 is the later SID, found in the C64C and the C128D. It is pin-for-pin identical to the 6581 except for the analogue supply: +9 V on pin 28, not +12 V. Fitting an 8580 into a 6581 socket without dropping pin 28 to 9 V will eventually kill it — adapter boards that regulate the 12 V down to 9 V exist for exactly this swap. The filter capacitors differ too: the 6581 wants 470 pF on CAP1A/B and CAP2A/B, the 8580 wants 22 nF. Swap the chip without swapping the caps and the filter sounds too open.
The 8580 is a cleaner, quieter part: much less background hiss, a filter that actually tracks the datasheet curve, and working combined waveforms. The trade-off is the loss of the 6581 digi-playback trick — volume-register sample playback is very quiet on an 8580, so some demos and games lose their sampled sound. Pin 25 is a separate +5 V supply for the digital side and pin 28 feeds the analogue side.
- Check pin 25 (VCC) at 5 V and pin 28 (VDD) at 9 V. A 12 V VDD will eventually kill an 8580; a missing VDD gives silence.
- No sound with a good /CS and PHI2 usually means a dead SID. One voice missing means the chip is partially failed and is not repairable.
- Check pin 27 (AUDIO OUT) for its DC bias — roughly half the pin 28 supply — before blaming the chip. A shorted output coupling capacitor mimics a dead SID.
- If the filter sounds wrong after a chip swap, check the filter capacitors (pins 1-4): the 8580 wants 22 nF, not the 6581 470 pF.
- Sampled sound (digi-drum) very quiet or missing is normal on an 8580 — the volume-register playback trick is much quieter than on the 6581.