External Timer Registers; Prescaler Register; Table 5-25 Prescaler Register - SMART Embedded Computing Penguin Edge MVME250 Series Installation And User Manual

Memory Maps and Registers
5.6

External Timer Registers

The MVME2502 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 register:
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 5-25 Prescaler Register

REG Prescaler Register - 0xFFC80100
Bit
15
Field
RSVD
OPER R/W
RESET 0x00e7
The prescaler provides the clock required by each of the three times. The tick timers require
a 1MHz clock input. The input clock to the prescaler is 25MHz. The default value is set for
0x00E7, which gives 1MHz reference clock for 25MHz input clock source.
114
14 13 12 11
RSVD RSVD RSVD RSVD
10 9 8
RSVD RSVD RSVD
MVME2502 Installation and Use (6806800R96L)
Memory Maps and Registers
7 6 5 4 3 2 1 0
Prescaler Register (8-bits)