NEC uPD765A floppy disk controller pinout

DIP-40. Floppy disk controller for the internal 3 in drive and drive B

Runs from a 4 MHz clock on the CPC (pin 19), not the 8 MHz of the datasheet, so it works at the 250 kbit/s MFM rate of the 3 in drive. Driven by polling: DRQ, INT and VCO are not connected, /DACK is held HIGH, and TC and RESET come from the same reset buffer. Ports &FB7E (status) and &FB7F (data); the drive motor is switched by a latch at &FA7E. The FDC9216 data separator (IC202) feeds it RDD and the 250 kHz RDW window. Before suspecting it, replace the drive belt and check the 12 V lead.

Open the interactive 765 pinout

Pins

Pin	Name	Type	Signal
1	RESET	ctrl	Reset, active HIGH: idles the FDC and drives the drive lines LOW.
2	/RD	ctrl	Read strobe from the CPU.
3	/WR	ctrl	Write strobe from the CPU.
4	/CS	ctrl	Chip select (74LS132 decode of &FB7x).
5	A0	addr	LOW = main status register, HIGH = data register.
6	DB0	data	Data bus bit 0.
7	DB1	data	Data bit 1.
8	DB2	data	Data bit 2.
9	DB3	data	Data bit 3.
10	DB4	data	Data bit 4.
11	DB5	data	Data bit 5.
12	DB6	data	Data bit 6.
13	DB7	data	Data bit 7.
14	DRQ	ctrl	DMA request. Not connected on the CPC.
15	/DACK	ctrl	DMA acknowledge. Held HIGH on the CPC.
16	TC	ctrl	Terminal count, active HIGH; tied to the reset buffer on the CPC.
17	IDX	ctrl	Index pulse from the drive.
18	INT	ctrl	Interrupt request. Not connected on the CPC (polled).
19	CLK	clock	Clock; 8 MHz in the datasheet, 4 MHz on the CPC.
20	GND	ground	0 V.
21	WCK	clock	Write clock (data rate) from the clock divider.
22	RDW	clock	Read data window from the data separator.
23	RDD	data	Read data from the data separator.
24	VCO	ctrl	VCO sync to a PLL. Not connected on the CPC.
25	WE	ctrl	Write enable to the drive.
26	MFM	ctrl	MFM mode HIGH, FM LOW. Not connected on the CPC.
27	HD	ctrl	Head (side) select.
28	US1	ctrl	Unit select bit 1.
29	US0	ctrl	Unit select bit 0: drive A or B.
30	WDA	data	Write data to the drive.
31	PS1	ctrl	Write precompensation status bit 1.
32	PS0	ctrl	Write precompensation status bit 0.
33	FLT/TR0	ctrl	Fault (read/write mode) or track 0 (seek mode) from the drive.
34	WP/TS	ctrl	Write protect or two-side from the drive.
35	RDY	ctrl	Drive ready.
36	HDL	ctrl	Head load. Not connected on the CPC.
37	FR/STP	ctrl	Fault reset or step pulses.
38	LCT/DIR	ctrl	Low current or step direction.
39	RW/SEEK	ctrl	HIGH = seek mode, LOW = read/write mode.
40	VCC	power	+5 V.

Fitted in

Amstrad CPC 664 IC201 (uPD765AC, Amstrad 40018)
Amstrad CPC 6128 IC201 (uPD765AC-2; Z765APS on later boards)

NEC uPD765A floppy disk controller pinout

Pins

Fitted in

Sources