Programming Model

Programming the Tick Timers

There are four programmable tick timers in the MC2 chip. These timers are identical in function to the timers implemented in the PCCchip2 and the VMEchip2.

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Tick Timer 1 and 2 Compare and Counter Registers

The Tick Timer Counter is compared to the Compare Register. When they are equal, an interrupt is sent to the local bus interrupter and the overflow counter is incremented. If the clear on compare mode is enabled, the counter is also cleared. For periodic interrupts, the following equation should be used to calculate the compare register value for a specific period

(T).

T (μs) = Compare Register

When programming the tick timer for periodic interrupts, the counter should be cleared to zero by software and then enabled. If the counter does not initially start at zero, the time to the first interrupt may be longer or shorter than expected. The rollover time for the counter is 71.6 minutes.

The Tick Timer Counter, when enabled, increments every microsecond. Software may read or write the counter at any time.

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Motorola MVME172 manual Programming the Tick Timers, Tick Timer 1 and 2 Compare and Counter Registers