Artesyn Embedded Technology MVME7100ET, Programmer'S Reference Manual

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Register Descriptions
MVME7100ET Single Board Computer Programmer’s Reference (6806800K88B )
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3.1.24 External Timer Registers
The MVME7100ET provides a set of tick timer registers for access to the four external timers
implemented in the timers/registers PLD. Note that these registers are 32-bit registers and are
not byte writable. The following sections describe the external timer prescaler and control
registers.
3.1.24.1 Prescaler
The Prescaler Adjust value is determined by this 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.
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.
TEST2 A read from this address will return the complement of the data pattern in Test Register 1. A write
to this address will write the uncomplemented data to register TEST1.
Table 3-25 Prescaler Register
REG Prescaler Register - 0xF202 0000 (8 bits of a 32-bit register)
BIT 7 6 5 4 3 2 1 0
Field Prescaler Adjust
OPER R/W
RESET $E7