Lsb Prescaler Count Register; Prescaler Clock Adjust Register - Motorola MVME162FX Programmer's Reference Manual

MC2 Chip

LSB Prescaler Count Register

3
ADR/SIZ
BIT
NAME
OPER
RESET

Prescaler Clock Adjust Register

3-18
This register is used to generate the 1 MHz clock for the four tick
timers. This register is read-only. It increments to $ff at the
processor frequency, then it is loaded from the Prescaler Clock
Adjust Register.
31
This register adjusts the prescaler so that it maintains a 1 MHz clock
source for the tick timers. To provide a 1 MHz clock, the prescaler
adjust register should be programmed based on the following
equation:
Prescaler Clock Adjust Register = 256 - processor clock (MHz)
For example, for operation at 25 MHz the prescaler value is $E7,
and at 32 MHz it is $E0.
Non-integer processor clocks introduce an error into the specified
times for the tick timers. The tick timer clock can be derived by the
following equation:
Tick clock = processor clock / (256 - prescaler value)
The maximum clock frequency for the tick timers is the processor
clock divided by two. The value $FF is not allowed to be
programmed into this register. If a write with the value of $FF
occurs to this register, the cycle terminates correctly but the register
remains unchanged.
$FFF42014 (8 bits)
. . .
LSB Prescaler Count
R
X
24