Technical data

MVME4100 Single Board Computer Programmer’s Reference (6806800H19B)

3.1.25 External Timer Registers

The MVME4100 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.

3.1.25.1 Prescaler Register

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 3-28 Prescaler Register

REG Prescaler Register - 0xF202 0000 (8 bits of a 32-bit register)

BIT7 654321 0

Field Prescaler Adjust

OPER R/W

RESET $E7