Seagate ST212 - 5.7 Fault Detection: PC Board 20292-XXX; 5.7.1 Voltage and Head Select Comparator; 5.7.2 Write Fault Reset

5.6.1.1
WRITE CURRENT INTERRUPTION
Any of the following conditions will cause Write Current to be inhibited when
Write Gate is true:
1. Multiple heads selected;
2. No head selected
3. SEEK
COMPLETE false
4. READY false
5. DC Voltages out of tolerance
6. A Step pulse is received
5
iiiii1i1
.7 . -iiiIIIIiF-lJ ... Uiliiiii~ECTION: PC BOARD 2.0292-XXX
OC POWER
(interface)
•
MICROPROCESSOR
-
RESET
VOLTAGE COMPARATOR
HEAD SELECT COMPARATOR
HEAD SELECT
~
(interface)
READIWRITE
LSI (IC6H)
WRITE FAULT
-
(interface)
WRITE GATE
SEEK COMPLETE
1
READY
(interface)
FIGURE 17:
Fault Detection
PC Board 20292-XXX
5.7.1
VOLTAGE AND HEAD SELECT COMPARATOR
The Read/Write LSI (IC 6H) continually monitors the +5 and + 12 Volt lines
for a low voltage condition.
If + Volts > 15070 low or + 12 is > 20070 low, the
DC-unsafe signal is activated (IC 6H,
pin 25) causing:
1. Write current to be disabled
2.
The microprocessor is reset
3. ·The fault line is activated (IC 6H,
pin 24)
4.
The heads are deselected
If multiple heads are selected, the Read/Write LSI will disable the write circuitry
and send a Write Fault to the interface (IC 6H, pin 24).
5.7.2
WRITE FAULT RESET
A selectable option is provided to clear a, Write Fault. The standard configura-
tion resets the Write Fault latch when Write Gate is dropped and reasserted (af-
ter the detected fault has been cleared). Shorting pins Il and 12 at connector
J9 causes the Write Fault latch to be reset when DRIVE SELECT is dropped
and reasserted after the detected fault has been cleared.
20
ST212 PRODUCT MANUAL/Rev.- B