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External Timer Registers
6.2.16
External Timer Registers
The MVME3100 provides a set of tick timer registers for access to the four external timers
implemented in the timers/registers PLD. These registers are 32-bit registers and are not
byte writable. The following sections describe the external timer prescaler and control
registers.
6.2.16.1 Prescalar Register
The prescaler provides the clock required by each of the four timers. The tick timers require
a 1MHz clock input. The input clock to the prescaler is 25MHz. The default value is set for
$E7, which gives a 1MHz reference clock for a 25MHz input clock source.
Table 6-17 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.
6.2.16.2 Control Registers
The prescaler provides the clock required by each of the four timers. The tick timers require
a 1MHz clock input. The input clock to the prescaler is 25MHz. The default value is set for
$E7, which gives a 1MHz reference clock for a 25MHz input clock source.
Table 6-18 Tick Timer Control Registers
REG
BIT
FIELD
116
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
MVME3100 Single Board Computer Installation and Use (6806800M28H)
4
3
9
8
7
6
2
1
5
4
3
2
Memory Maps
0
1
0
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