Programmable Interval Timer
Élan™SC520 Microcontroller User’s Manual 16-7
■ Driving an external 1.19318-MHz clock on the CLKTIMER pin—A system designer can
choose to supply an external clock source frequency of 1.19318 MHz on the CLKTIMER
pin. This pin must be specifically configured for this functionality by the system boot
code during the system boot process, prior to configuring the PIT. The CLK_PIN_DIR
bit in the Clock Select (CLKSEL) register (MMCR offset C26h) is used for this purpose.
16.6 INITIALIZATION
At system reset, the state of the PIT itself is undefined. The mode, count value, and output
of all channels are undefined. Each PIT channel must be programmed before it can be
used. To prevent superfluous interrupts, each PIT channel must be configured prior to
enabling interrupts on the Am5
x
86 CPU.
1. Write a control word into the PIT Mode Control (PITMODECTL) register (Port 0043h).
2. Write an initial count into the PIT Channel x Count (PITxCNT) register of the PIT channel
being programmed. The control word determines the format of the initial count.
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