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Chapter 1 Board Description and Memory Maps
Prescalar Register
The prescaler provides the clock required by each of the four timers. The tick timers require a 1 MHz
clock input. The input clock to the prescaler is 25 MHz. The default value is set for $E7, which gives a
1 MHz reference clock for a 25 MHz input clock source.
Table 1-19. Prescalar Register
REG
BIT
FIELD
OPER
RESET
Prescalar Adjust
The prescaler adjust value is determined by the following formula:
Prescaler adjust = 256 - (CLKIN/CLKOUT)
where CLKIN is the input clock source in MHz and CLKOUT is the desired output clock reference
in MHz.
Control Registers
The prescaler provides the clock required by each of the four timers. The tick timers require a 1 MHz
clock input. The input clock to the prescaler is 25 MHz. The default value is set for $E7, which gives a
1 MHz reference clock for a 25 MHz input clock source.
Table 1-20. Tick Timer Control Registers
REG
BIT
FIELD
OPER
RESET
ENC
Enable counter. When this bit is high, the counter increments. When this bit is low, the counter does
not increment.
20
MVME3100 Programmer's Guide (V3100A/PG1)
Prescalar Register - 0xE2020000 (8 bits of 32)
7
6
5
Prescalar Adjust
R/W
$E7
Tick Timer 1 Control Register - 0xE2020010 (32 bits)
Tick Timer 2 Control Register - 0xE2020020 (32 bits)
Tick Timer 3 Control Register - 0xE2020030 (32 bits)
Tick Timer 4 Control Register - 0xE2020040 (32 bits)
31
...
11
10
9
R/W
0
...
0
0
0
4
3
2
8
7
6
5
0
0
0
0
1
0
4
3
2
1
0
0
0
0
0
0
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