Motorola MVME172 - Manual (Page 236)

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MC2 Chip
3
32-bit Prescaler Count Register
The prescaler register is used to clock timing functions in the MC2 chip.
The lower 8 bits of the prescaler is programmed to generate an output with
a one microsecond period. Refer to the section on the LSB Prescaler Count
Register under Programming the Tick Timers in this chapter. The upper 24
bits are used to clock the local bus access timer and watchdog timer. To
facilitate testing, the upper 24 bits can be written to. Writes to this register
must be 32 bits.
LSB7-0 The least significant bits of the 32-bit prescaler. These bits
are read only. They are duplicated in the memory map in
the MC2 chip at $FFF42014.
MSB31-8 The most significant bits of the prescaler.
Note that for the "No VMEbus Interface" option, the 32-
bit Prescaler Count Register is located at $FFF40064 in
addition to $FFF4204C. This means that this register is
located at the same address ($FFF40064) on an
MVME172 with the VMEchip2 as well as an MVME172
without the VMEchip2. This feature is provided for those
applications which require a Prescaler Count Register to
run on all MVME172 versions.
ADR/SIZ $FFF4204C (32 bits)
BIT 31 . . . 8 7-0
NAME MSB LSB
OPER R/W R
RESET 0 P