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
- 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.
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