fdc-expert

Expert on NEC µPD765 Floppy Disk Controller for ES-1841. Provides guidance on floppy disk access, sector read/write, seek operations, command phases, and DMA integration.

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SKILL.md

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.