Programmable Interrupt Timers (PIT0–PIT1)
MCF52277 Reference Manual, Rev. 1
27-6
Freescale Semiconductor
When the PCSR
n
[OVW] bit is set, the counter can be directly initialized by writing to PMR
n
without
having to wait for the count to reach 0x0000.
Figure 27-5. Counter Reloading from the Modulus Latch
27.3.2
Free-Running Timer Operation
This mode of operation is selected when the PCSR
n
[RLD] bit is clear. In this mode, the counter rolls over
from 0x0000 to 0xFFFF without reloading from the modulus latch and continues to decrement.
When the counter reaches a count of 0x0000, PCSR
n
[PIF] flag is set. If the PCSR
n
[PIE] bit is set, PIF flag
issues an interrupt request to the CPU.
When the PCSR
n
[OVW] bit is set, counter can be directly initialized by writing to PMR
n
without having
to wait for the count to reach 0x0000.
Figure 27-6. Counter in Free-Running Mode
27.3.3
Timeout Specifications
The 16-bit PIT counter and prescaler supports different timeout periods. The prescaler divides the internal
bus clock period as selected by the PCSR
n
[PRE] bits. The PMR
n
[PM] bits select the timeout period.
Eqn. 27-1
27.3.4
Interrupt Operation
shows the interrupt request generated by the PIT.
0x0002
0x0001
0x0000
0x0005
0x0005
PIT CLOCK
COUNTER
MODULUS
PIF
0x0002
0x0001
0x0000
0xFFFF
0x0005
PIT CLOCK
COUNTER
MODULUS
PIF
Timeout period
PRE[3:0] (PM[15:0] 1)
+
×
f
sys 2
⁄
×
=
Содержание MCF52277
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