Tandy 1400LT Service Manual page 229

INPUT SIGNALS
The FDD has the following input lines.
(1) DRIVE SELECT 0 TO 1
(2) MOTOR ON
(3) DIRECTION
(4) STEP
(5) WRITE DATA
(6) WRITE GATE
(7) SIDE 1 SELECT
DRIVE SELECT 0 TO 1
Two input lines are provided for drive select, DRIVE SELECT 0 TO 1.
Up to two drives can be daisy chained by setting the drive select switch on the PCB.
A "Low" level on input signal DRIVE SELECT 0 enables the drive to operate when the drive select switch is set to
"DSO".
The other drives in the chain can be selected in the same way.
The setting position on the select switch must be different for each drive in the chain.
MOTOR ON
The Spindle Motor starts when this signal becomes "Low".
DIRECTION
This signal determines the direction of R/W Heads movement by the following:
"High" Level: Out (towards Track 00)
"Low" Level: In (towards Track 79)
STEP
This line causes the R/W Heads to move.
The period of a STEP pulse must be a minimum of 6ms.
A (21 ms) delay following the last STEP pulse is required before the read or write operation can be initiated.
A (21 ms) delay following the last STEP pulse is required for the next STEP pulse when the DIRECTION is
changed.
The following examples describe several cases that make STEP pulses valid or invalid.
(1) STEP pulses towards the outside after the TRACK 00 signal has been generated are invalid.
(2) STEP pulses whose intervals are less than 6 ms may cause seek errors.
(3) A STEP pulse should be generated at more than 21 msec. when DIRECTION signal has been reversed.
Fig. C-5 shows step pulse timing.
c-8