UPD765 signal description

MZ3500

Pin No.	Signal name	I/O
40	Vcc	-
20	GND	-
19	0	I
1	RESET	1
4	CS	1
13 - 6	DB7 ~ DBO	I/O
3	WR
		'
2	RD	1
18	INT	o
5	AO	1
14	DRQ	o
15	DACK	1
29,28	USD, 1	0
26	MFM	o
24	SYNC	o
39	RW/SEEK	o
36	HOLD	0
27	SIDE	0
38	LCT/DIR	0
37	FLTR/STEP	o
35	READY	1
34	WPRT/2 SIDE	1
17	INDEX	'
		'
33	FLT/TRKO	1
16	TC	1
30	WDATA	0
25	WE	o
21	WCLK	1

Function

+5V

Single phase, TTL level clock

Set the FDC into an idle state, and all drive unit interface outputs, except PSO, 1 , and WDATA (don't care), are set to low level In addition, INT and DRW outputs are set to low level DB goes into an input state.

Validates RD and WR signals

Bidirectional, tri-state data bus

Control signal to write data to the FDC via the data bus

Control signal to read data from the FDC via the data bus

The signal used to indicate a service request from the FDC It is issued at every byte in the non- DMA mode, or upon completion execution of a command in the DMA mode

The signal used to select the status register or data register of the FDC for access via the data bus. When 0, it selects the status register When 1. it selects the data register.

FDC to memory data transfer request signal in the DMA mode

The signal that indicates use of the DMA cycle During the DMA cycle, it functions identically toCS.

Drive unit select signal, with which up to four drive units can be selected.

The signal used to designate the operation mode of the VFO circuit When 0, the MFM mode is assigned. When 1, the FM mode is assigned

The signal used to designate the operation mode of the VFO circuit When 1, it permits reading operation. When 0, it prohibits reading operation

Signal used to discriminate the read/write signal from the seek signal that used for drive unit interfacing signal. When 0, it indicates RW When 1 , it indicates

Signal used to load the read/write head

Signal used to select head #0 and head #1 for the double-sided floppy disk drive unit. When 0, it selects head 0. When 1, it selects head 1.

When the RW/seek signal is operating as RW, the signal works as LCT which indicates that the read/write head is selecting the cylinder above 43. When the RW/SEEK is operating as SEEK, it works as DIR which indicate seek direction When 0. seek is made towards outer side When 1, seek is made towards inner side

When the RW/SEEK signal functions as RW, it works as F LTR which resets any fault condition as the seek step signal.

Signal used to indicate that the drive unit is ready for operation

When the RW/SEEK signal is operating as RW, it function as WPRT which indicates that the drive unit or the floppy disk is write protected. When the RW/SEEK is function as the SEEK signal produces 2 SIDE which indicates that a double sided media is in use.

Signal to indicate the physical start point of the track.

When the RW/SEEK signal is operating as RW. it works as FLT which indicates that the drive unit is in a fault condition. When the RW/SEEK is operating as SEEK, it works as TRKO which indicates that the read/write head is on cylinder 0.

Signal used to indicate the termination of a read or write operation

Data written on the floppy disk consists of clock bits and data bits

Signal to indicate write enable to the drive unit

Data write timing signal which is 250kHz in the FM mode or 500kHz in the MFM mode

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