Servicing Personal Computers, 3rd Edition

278 Servicing Personal Computers

Disk interface

The ST series of computers employ the popular Western Digital 1772 floppy disk controller.

The ST configuration can cope with either:

(a) one internal and one external floppy disk drive (e.g. 1040STFM); or

(b) two external floppy disk drives (e.g. 520ST).

It is important to note that, whilst most of the floppy disk signals are produced by the Ί772

FDC,

drive and side selection signals are provided by the programmable sound synthesizer

chip (the Yamaha YM1249 PSG).

The 68000 CPU reads and writes to the

1

772 FDC by means of the DMA controller. The

FDC interrupts the CPU by means of the INTR lin ...