WD 1770/1772
FLOPPY DISK CONTROLLER/FORMATTER



PIN DESC DESCFUNCTION
1 CSCHIP SELECT A logic low on this input selects the chip and enable Host communication with the device.
2 R/W READ/WRITE A logic high on this input controls the placement of data on the D0-D7 lines from a selected register, while a logic low causes a write operation to a seleeted register.
3,4 A0,A1 ADDRESS 0,1 These two inputs select a register to Read/Write data: 
   CS  A1  A0     R/W=1       R/W=0
   0   0   0   Status Reg  Command Reg
   0   0   1   Track Reg   Track Reg
   0   1   0   Sector Reg  Sector Reg
   0   1   1   Data Reg    Data Reg
5-12 DAL0-DAL7 DATA ACCESS LINES 0 THRU 7 Eight bit bidirectional bus used for transfer of data, control, or status. This bus is enabled by CS and R/W. Each line will drive one TTL load.
13 MR MASTER RESET A logic low pulse on this line resets the device and initializes the status register (internal pull-up).
14 GND GROUNDGround.
15 Vcc POWER SUPPLY +5V ± 5% power supply input.
16 STEP STEP The STEP output contains a pulse for each step of the drive's R/W head. The WD 1770 and WD1772 offer different step rates.
17 DIRC DIRECTION The DIRECTION output is high when stepping in towards the center of the diskette, and low when stepping out.
18 CLK CLOCK This input requires a free-running 50% duty cycle clock (for internal timing) at 8MHz ± 1%.
19 RD READ DATA This active low input is the raw data line containing both clock and data pulses from the drive.
20 MO MOTOR ON Active high output used to enable the spindle motor prior to read, write or stepping operations.
21 WG WRITE GATE This output is made valid prior to writing on the diskette.
22 WD WRITE DATA FM or MFM clock and data pulses are placed on this line to be written on the diskette.
23 TR00 TRACK00 This active low input informs the WD1770 that the drive's R/W heads are positioned over Track Zero (internal pull-up).
24 IP INDEX PULSE This active low input informs the WD1770 when the physical Index Hole has been encountered on the diskette (internal pull-up).
25 WPRT WRITE PROTECT This input is sampled whenever a Write Command is received. A logic low on this line will prevent any Write Command from executing (internal pull-up).
26 DDEN DOUBLE DENSITY ENABLE This input pin selects either single (FM) or double (MFM) density. When DDEN = 0, double density is selected (internal pull-up).
27 DRQ DATA REQUEST This active high output indicates that the data register is full (on a READ) or empty (on a Write operation).
28 INTRQ INTERRUPT REQUEST This active high output is set at the completion of any command or reset or read of the status register.