MPI 40 Series - Write;Er~Se; Read Operation

(area B7) and a positive voltage greater than +6V is placed on pin
13, the base of the head 0 enable transistor. This transistor
gates a positive voltage to the center top of head (IJ to enable
it. The base of the head 1 enable trans is tor, pin 10 (area C6)
would be low at this time which would reverse bias the transistor
and cause a ground to be sent to the center tap of the head 1 to
disable it. Changing polarity of the SIDE SELECT signal changes
the polarity of the center taps of both heads. When switching
sides from one to the other after the SIDE SELECT line changes
state, a 100 us delay is required before read or write operation
can be initiated. Figure 3-6 shows the use of SIDE SELECT prior to
a read operation.
3.6.6 Write/Erase
Encoded (FM or MFM) data will be written on the disk by:
A. Selecting the proper drive.
B. Selecting a read/write head (if necessary).
C. Activating the WRITE GATE line (OV to .4V).
D. Placing data to be written on the WRITE DATA line.
The timing characteristics required to initiate a write operation
are shown in Figure 3-8. The timing requirement for FM encoded
data to be written is shown in Figure 3-12. These timing require-
ments ensure that the selected read/write head is positioned and
stabilized at the desired track prior to writing and to ensure flux
change occurrence at the desired transfer rate. After the drive
and head has been selected the WRITE GATE signal (Pl-40) must go
low (page 3, area B7). This makes U28-6 go high; U27-6 go low; and
U31-10 go low disabling the step circuitry. Also, U28-6 going high
make U31-3 (area B6) go low; and U29-12 go high to develop the +
Write Enable signal. The + Write Enable signal on page 2 (area B7)
enables write flip flop Ul2 and the erase circuitry. WRITE DATA
clocks the write flip flop, Ul2, which changes states with each
data bit to be written. On the flip flop's output through open-
collector Ul pin 2 and 6, any low level signal will pass through
its respective transistor, forward bias its associated diode (CR5
and CR9), and pass current through the co~l. On the next write
data bit the flip flop will toggle, causing current to flow in the
opposite direction; thereby storing a high data bit as a flux
reversal on the diskette.
3.6.7 Read Operation
Data can be read from the disk drive by:
A. Selecting the drive.
3-21