fdc-expert

name	fdc-expert
description	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.

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

1. Command: Write to 3F5h (RQM=1, DIO=0)
2. Execution: DMA transfer
3. 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.