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
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).
U S 0 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.
The READY input indicates that the FDD is ready to re-
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
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.
The RW/SEEK output specifies the read/write mode
when low, and the seek mode when high.
+5 V power supply.