Seagate ST212 - 5.8 Fault Detection: PC Board 20243-XXX; 5.8.1 Voltage Comparator; 5.8.2 Head Select Comparators

OC POWER
1
_1
VOLTAGE
1
-
MICROPROCESSOR 1
1
1
COMPARATORS
1
---
RESET
,
HEAD SELECT
1
1
WRITE
H
INTERFACE
1
COMPARATOR
1
CIRCUIT WRITE FAULT
-
1
1
1
WRITE GATE,
SEEK COMPLETE, READY
1
FIGURE 18:
FaultOetection
PC Board 2D243-XXX
FAULT DETECTION: PC BOARD 20243-XXX
VOLTAGE COMPARATOR
5.8
5.8.1
Comparators at IC 70 continually monitor both the +5 and + 12 Volt lines
to detect a low voltage condition.
If + 5V is > 15070 low or + 12V is > 20070
low, Write current will be disabled, the microprocessor reset, the fault line acti-
vated and the beads deselected.
HEAD SELECT COMPARATORS
5.8.2
When a single head is selected (normal operation), IC 70 (pins 1 and 2) will
be high.
If more than one head is selected, the voltage will increase at 70 (pin
4) forcing its output low. An attempt to write with no head selected will decrease
the voltage at
70 (pin 4) forcing its output low. A low on either comparator
will disable the Write circuitry and send a Write Fault to the interface.
,ST212 PRODUCT MANUAL/Rev. B 21