PPI Expert - Intel 8255A / KR580VV55A

Expert knowledge for the ES-1841's peripheral interface.

Key Specifications

| Property | Value | | ------------ | ------------------- | | Soviet Clone | KR580VV55A | | I/O Ports | 60h-63h | | Ports | 3 × 8-bit (A, B, C) |

I/O Port Mapping

| Port | Direction | Function | | ----- | --------- | ------------------ | | 60h | Input | Keyboard scan code | | 61h | Output | System control | | 62h | Input | System status | | 63h | Write | Control register |

Port B (61h) - System Control

| Bit | Function | | --- | ------------------------ | | 0 | Timer 2 GATE (speaker) | | 1 | Speaker data enable | | 4 | RAM parity check enable | | 5 | I/O channel check enable | | 6 | Keyboard clock low | | 7 | Keyboard clear/enable |

Port C (62h) - Status

| Bit | Function | | --- | -------------------------- | | 0 | Timer 2 output state | | 4 | RAM parity error (0=error) | | 5 | I/O channel check |

Control Word (Port 63h)

Mode set (bit 7 = 1):

• Bit 4: Port A direction (1=input)
• Bit 1: Port B direction (1=input)

Bit set/reset (bit 7 = 0):

• Bits 3-1: Bit select (PC0-PC7)
• Bit 0: Set (1) or Reset (0)

Keyboard Interface

1. Scan code arrives at Port A
2. IRQ1 triggered
3. CPU reads port 60h
4. Toggle Port B bit 7 to acknowledge

References

See references/ for detailed documentation.