SMART Embedded Computing MVME2502, Инструкция по установке и эксплуатации

Страница: 114 / 150

114 MVME2502 Installation and Use (6806800R96L)
Memory Maps and Registers
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.
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.
Table 5-25 Prescaler Register
REG Prescaler Register - 0xFFC80100
Bit
15 14 13 12 11 10 9 8
7 6 5 4 3 2 1 0
Field
RSVD RSVD RSVD RSVD RSVD RSVD RSVD RSVD Prescaler Register (8-bits)
OPER R/W
RESET 0x00e7