UPD765B datasheet(3/17 Pages) NEC

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NEC

uPD765A/uPD765B

WCLK (Write Clock)

The WCLK input sets the data write rate to the FDD. It is

500 kHz for FM, 1 MHz for MFM drives, for 8 MHz opera-

tion of the FDC; 250kHz FM or 500 kHz MFM for 4 MHz

FDC operation.

This signal must be input for read and write cycles

WCLK’s rising edge must be synchronized with CLK’s

rising edge, except for the

uPD765B.

WINDOW (Read Data Window)

The WINDOW input is generated by the phase-locked

loop (PLL). It is used to sample data from the FDD and in

distinguishing between clock and data bits in the FDC.

RDATA (Read Data)

The RDATA input is the read data from the FDD,

containing clock and data bits. To avoid a deadlock

situation, input RDATA and WINDOW together.

WDATA (Write Data)

WDATA is the serial clock and data output to the FDD.

WE (Write Enable)

The WE output enables write data into the FDD.

SYNC (VCO Sync)

The SYNC output inhibits the VCO in the PLL when low,

enables it when high.

MFM (MFM Mode)

The MFM output shows the

VCO’s

operation mode. It is

high for MFM, low for FM.

SIDE (Head Select)

Head 1 is selected when the SIDE output is 1 (high), head

0 is selected when SIDE is 0 (low).

US0 US1 (Unit Select 0,1)

The US0 and US1 outputs select up to 4 floppy disk drive

units using an external decoder.

PS0, PS1 (Preshift 0,1)

The PS0 and PS1 outputs are the write precompensation

request signals for MFM mode. They determine early,

late, and normal times for WDATA shifting.

READY (Ready)

The READY input indicates that the FDD is ready to re-

ceive data.

HDLD (Head Load)

The HDLD output is the command which causes the

read/write head in the FDD to contact the diskette.

FLT/TRKO (Fault/Track 0)

In the read/write mode, the FLT input detects FDD fault

conditions. In the seek mode, TRKO indicates track 0

head

position.

WPRT/2SlDE

(Write Protect/Two Side)

In the read/write mode, the WPRT input senses write

protected status (at the drive or media.)

In the seek

mode, 2SIDE

senses two-sided media.

FLTR/STEP

(Fault Reset/Step)

In the read/write mode, the FLTR output resets the fault

flip-flop in the FDD. In the seek mode, STEP outputs

step pulses to move the head to another cylinder. A fault

reset pulse is issued at the beginning or each Read or

Write command prior to the HDLD signal.

LCT/DlR (Low Current/Direction)

In the read/write mode, the LCT output indicates that

the R/W head is positioned at cylinder 42 or greater. In

the seek mode, the DIR output determines the direction

the head will move in when it receives a step pulse. If

DIR is 0, seeks are performed in the outward direction;

DIR is 1, seeks are performed in the inward direction.

RWlSEEK

(Read/Write/Seek)

The RW/SEEK output specifies the read/write mode

when low, and the seek mode when high.

GND (Ground)

Ground.

Vcc(+5v)

+5 V power supply.

5-5

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