Apple Lisa - Non-Volatile Memory; Battery

Confidential
Lisa Hardware Reference Manual 7-Jul-81
FLOPPY CONTROLLER INTERRUPT SOURCE
D7 Set if D6, D5, or D4 is set
D6 Set if RWTS is complete for Drive 1
D5 Set when the Drive 1 Button is pushed
D4 Set when Drive 1 signals "disk in place"
D3 Set if D2, D1, or DO is set
D2 Set if RWTS is complete for Drive 0
D1 Set when the Drive 0 Button is pushed
DO Set when Drive 0 signals "disk in place"
The 68000 can clear any of the bits in this word with the Clear Interrupt
Status command. D7 and D3 remain set as long as any associated bit is set.
The Interrupt Mask byte at SOOC083 determines which drive can interrupt
the 68000. Only bits 7 (Drive 1) and 3 (Drive 0) are used. The Set
Interrupt Mask command (S86) sets the bits of this mask on the basis
of the operand byte at $00C003. The Clear Interrupt Mask command (S87)
clears these bits on the same basis. If interrupts are masked off,
no interrupts can occur until they are enabled again.
NON-VOLATILE MEMORY
The 1K floppy disk controller shared memory RAM is backed up by the
same power source that backs up the clock/calendar circuit. The last
.64 words in the 6505's page 0 are- reserved for the "parameter memory"
of the sys~m. Since the 6.5.05 cloes ftO't use these bytes, the 68000 can
store data here which it wants to be able to access intact when the
system is powered on. The reserved memory appears at the 68000
locations $00C181 - $00C1FF.
THE BATTERY
The disk controller also controls the charging current for the battery
back up. Ni-Cd batteries last much longer if the charging current
is pulsed with a 50% duty cycle at 200% of the normal charging current.
While the disk controller is waiting for a command, it cycles the
charging current at about ten times per second. The charging current
is turned off while the controller is executing a co~nd.
As long as the system is plugged in, the backup battery is not in use.
If there is a power failure, or the system is unplugged, the battery
can last about 20 hours.
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