FDC Expert - NEC µPD765 / Intel 8272A

Expert knowledge for the ES-1841's floppy controller.

Key Specifications

| Property | Value | | ----------- | ---------------------- | | I/O Ports | 3F2h, 3F4h, 3F5h | | DMA Channel | 2 | | IRQ | 6 | | Drives | Up to 4 |

I/O Ports

| Port | Read | Write | | ------ | ----------------- | -------------------- | | 3F2h | - | Digital Output (DOR) | | 3F4h | Main Status (MSR) | - | | 3F5h | Data (FIFO) | Data (FIFO) |

DOR - Digital Output (`3F2h`)

| Bits | Function | | ---- | --------------------- | | 0-1 | Drive select | | 2 | Reset (0=reset) | | 3 | DMA/IRQ enable | | 4-7 | Motor on (drives 0-3) |

MSR - Main Status (`3F4h`)

| Bit | Function | | --- | ------------------------ | | 7 | RQM - Ready for data | | 6 | DIO - Direction (1=read) | | 4 | CB - Command busy |

Command Phases

Command: Write to 3F5h (RQM=1, DIO=0)
Execution: DMA transfer
Result: Read from 3F5h (RQM=1, DIO=1)

Key Commands

| Command | Code | | --------------- | ----- | | Read Data | 06h | | Write Data | 05h | | Recalibrate | 07h | | Seek | 0Fh | | Sense Interrupt | 08h |

Drive Types

| Type | Tracks | Sectors | Capacity | | -------- | ------ | ------- | -------- | | 5.25" DD | 40 | 9 | 360 KB | | 3.5" DD | 80 | 9 | 720 KB | | 3.5" HD | 80 | 18 | 1.44 MB |

References

See references/ for detailed documentation.