PIT Expert - Intel 8253 / KR580VI53

Expert knowledge for the ES-1841's timer subsystem.

Key Specifications

| Property | Value | | ------------ | -------------------- | | Soviet Clone | KR580VI53 | | Counters | 3 independent 16-bit | | I/O Ports | 40h-43h | | Clock Input | 1.193182 MHz |

I/O Ports

| Port | Description | | ----- | -------------- | | 40h | Counter 0 data | | 41h | Counter 1 data | | 42h | Counter 2 data | | 43h | Control Word |

Control Word Format

Bits 7-6: Counter select (00/01/10 = C0/C1/C2)
Bits 5-4: R/W (01=LSB, 10=MSB, 11=LSB+MSB)
Bits 3-1: Mode (0-5)
Bit 0:    BCD (0=binary)

Channel Assignments

| Ch | Function | Mode | Typical Count | | --- | ------------ | ---- | -------------- | | 0 | System Timer | 3 | 65536 (18.2Hz) | | 1 | DRAM Refresh | 2 | 18 (~66kHz) | | 2 | PC Speaker | 3 | Variable |

Operating Modes

• Mode 0: Interrupt on terminal count
• Mode 2: Rate generator (periodic pulse)
• Mode 3: Square wave generator (50% duty)

Timer Frequency Calculations

Output Frequency = 1193182 / Count
18.2 Hz = 1193182 / 65536

Speaker Control (Port 61h)

• Bit 0: Timer 2 GATE enable
• Bit 1: Speaker output enable

References

See references/ for detailed documentation.