Freescale Semiconductor MPC8260 - Manual (Page 176)

System Interface Unit (SIU)
MPC8260 PowerQUICC II Family Reference Manual, Rev. 2
4-4 Freescale Semiconductor
Figure 4-3. Timers Clock Generation
For details, see Section 40.2.4, “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