Sharp MZ-3500 - Manual (Page 53)

UPD765 signal description
MZ3500
Pin No. Signal name I/O Function
40 Vcc - +5V
20 GND -
0V
19 0 1
Single phase, TTL level clock
1 RESET 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.
4 CS 1 Validates RD and WR signals
13 ~ 6 DB7 ~ DBO I/O Bidirectional, tri-state data bus
3 WR 1 Control signal to write data to the FDC via the data bus
2 RD 1 Control signal to read data from the FDC via the data bus
18 INT 0 The signal used to indicate a service request from the F DC It is issued at every byte in the non-
DMA mode, or upon completion execution of a command m the DMA mode
5 AO 1 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.
14 DRQ о FDC to memory data transfer request signal in the DMA mode
15 DACK I The signal that indicates use of the DMA cycle During the DMA cycle, it functions identically
to CS.
29, 28 USO, 1 о Drive unit select signal, with which up to four drive units can be selected.
26 MFM 0 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
24 SYNC о The signal used to designate the operation mode of the VFO circuit When 1. it permits reading
operation. When 0, it prohibits reading operation
39 RW/SEEK о 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
36 HOLD о Signal used to load the read/write head
27 SIDE о 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.
38 LCT/DIR о 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
37 FLTR/STEP о When the RW/SEEK signal functions as RW, it works as F LTR which resets any fault condition
as the seek step signal.
35 READY 1 Signal used to indicate that the drive unit is ready for operation
34 WPRT/2 SIDE 1 When the RW/SEEK signal is operating as RW, it furtction 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.
17 INDEX
'
Signal to indicate the physical start point of the track.
33 FLT/TRKO 1 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/wnte head is on cylinder 0.
16 TC 1 Signal used to indicate the termination of a read or write operation
30 WDATA о Data written on the floppy disk consists of clock bits and data bits
25 WE о Signal to indicate write enable to the drive unit
21 WCLK 1 Data write timing signal which is 250kHz in the FM mode or 500kHz in the MFM mode
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