Read/Write Circuit - Fujitsu M2301B Manual

4.6.9 Read/Write Circuit
(1) General
This circuit consists of the head select circuit, write circuit, read circuit, and
VFO circuit.
(2) Head Select Circuit
This is the circuit which selects the designated data head from 4 heads in the
M2301, and from 8 heads in the M2302 in response to the head select signal
(HEAD SELECT 0 to 2) from the controller. A head is selected when +12V is
applied. When a head is not selected, OVis applied.
(3) Write Circuit
The block diagram of the write circuit is shown in Fig. 4.25.
(a) NRZ to MFM Encoding Circuit
The MFM recording method is used to write data on the disks. The encod-
ing circuit converts NRZ data from the controller. The output of this
encoding circuit is called Write Data Pulse (WOP) and is sent to the Write
Driver circuit. Fig. 4.26 shows the correlation between NRZ and MFM.
(b) Write Amplifier
This is the circuit which supplies the write current to the data head.
The WR ITE GATE signal, a write instruction from the controller, causes
the circuit to be turned on and off. If an error is detected by the write
fault detection circuit or the power loss detection circuit, the write ampli-
fier circuit is unconditionally turned off.
(c) Write Drive
. This is the circuit which switches the write current to the data head ac-
cording to WOP. The circuit receives the current from the write amplifier
and the MFM write data pulse from the encoding circuit.
(d) Write Fault Detection Circuit and Fault Latch
This is the circuit which detects the occurrence of an error during the
write operation. If any of the following conditions occur, the circuit sets
up the FAULT LATCH and transmits the WRITE FAULTto the control-
ler. The circuit also sets up the detail of an error and holds it until the
F AU L T CLEAR is received from the controller. The detail of an error can
be observed on test points on the printed board.
Error Status
The Check Terminal Set by
Fault Latch
Both WRITE GATE and READ GATE come at
RGF
the same time.
W RITE GATE comes when more than one head
MLT
is selected.
During the WR ITE operation, abnormal current
UNS
flows through the data head.
The WR ITE GATE signal comes when SEEK
SEK
COMPLETE is false.
The WR ITE GATE siganl comes when the unit
FRY
is not READY.
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