MPC8280 datasheet(176/1386 Pages) FREESCALE

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System Interface Unit (SIU)

MPC8280 PowerQUICC II Family Reference Manual, Rev. 1

4-4

Freescale Semiconductor

Figure 4-3. Timers Clock Generation

For details, see Section 41.2.4, “Port Pin Assignment Register (PPAR).” For proper time counter

operation, the user must ensure that the frequency of timersclk for TMCNT is 8,192 Hz by properly

selecting the external clock and programming BRG1 and the prescaler control bits in the time counter

status and control register (TMCNTSC[TCF]) and periodic interrupt status and control register

(PISCR[PTF]).

4.1.3

Time Counter (TMCNT)

The time counter (TMCNT) is a 32-bit counter that is clocked by timersclk. It provides a time-of-day

indication to the operating system and application software. The counter is reset to zero on PORESET reset

or hard reset but is not effected by soft reset. It is initialized by the software; the user should set the

timersclk frequency to 8,192 Hz, as explained in Section 4.1.2, “Timers Clock.”

TMCNT can be programmed to generate a maskable interrupt when the time value matches the value in

its associated alarm register. It can also be programmed to generate an interrupt every second. The time

counter control and status register (TMCNTSC) is used to enable or disable the various timer functions

and report the interrupt source. Figure 4-4 shows a block diagram of TMCNT.

PC[29]

PC[25]

CPM clock

PC[27]

PC[26]

Ports Programming

The user should select external clock and/or BRG1 programming

to yield either 4 MHz or 32 KHz at this point.

BRG1

Divide by 512

Divide by 4

PISCR[PTF]

TMCNTSC[TCF]

Ports Programming

timersclk for TMCNT

timersclk for PIT

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