External Timer Registers; Prescaler Register; Table 5-22 Prescaler Register - SMART Embedded Computing MVME2500 Installation & Use Manual

5.6

External Timer Registers

The MVME2500 provides a set of tick timer registers to access the three external timers
implemented in the timers/registers PLD. These registers are 32-bit and are word writable.
The following sections describe the timer prescaler and control registers:
5.6.1

Prescaler Register

The prescaler adjust value is determined by this formula:
Prescaler Adjust = 256-(CLKIN/CLKOUT)
CLKIN is the input clock source in MHz, and CLKOUT is the desired output clock reference
in MHz.

Table 5-22 Prescaler Register

REG
Bit
Field
OPER
RESET 0x00e7
The prescaler provides the clock required by each of the three times. The tick timers require
a 1 MHz clock input. The input clock to the prescaler is 25 MHz. The default value is set for
0x00E7, which gives a 1 MHz reference clock for a 25 MHz input clock source.
MVME2500 Installation and Use (6806800L01S)
Prescaler Register - 0xFFC80100
15 14 13 12
RSVD RSVD RSVD RSVD RSVD RSVD RSVD RSVD Prescaler Register (8-bits)
R/W
Memory Maps and Registers
11 10 9 8 7 6 5 4 3 2 1 0
103