Chapter 18 Periodic Interrupt Timer (S12PIT24B4CV2)
MC9S12XE-Family Reference Manual , Rev. 1.19
688
Freescale Semiconductor
Whenever the micro timer down-counter has counted to zero the PITMTLD register is reloaded and the
connected 16-bit modulus down-counters count one cycle.
Whenever a 16-bit timer counter and the connected 8-bit micro timer counter have counted to zero, the
PITLD register is reloaded and the corresponding time-out flag PTF in the PIT time-out flag (PITTF)
register is set, as shown in
. The time-out period is a function of the timer load (PITLD) and
micro timer load (PITMTLD) registers and the bus clock f
BUS
:
time-out period = (P 1) * (PITLD + 1) / f
BUS
.
For example, for a 40 MHz bus clock, the maximum time-out period equals:
256 * 65536 * 25 ns = 419.43 ms.
The current 16-bit modulus down-counter value can be read via the PITCNT register. The micro timer
down-counter values cannot be read.
The 8-bit micro timers can individually be restarted by writing a one to the corresponding force load micro
timer PFLMT bits in the PIT control and force load micro timer (PITCFLMT) register. The 16-bit timers
can individually be restarted by writing a one to the corresponding force load timer PFLT bits in the PIT
forceload timer (PITFLT) register. If desired, any group of timers and micro timers can be restarted at the
same time by using one 16-bit write to the adjacent PITCFLMT and PITFLT registers with the relevant
bits set, as shown in
.
Figure 18-20. PIT Trigger and Flag Signal Timing
Bus Clock
0
2
1
0
8-Bit Micro
2
1
0
2
1
0
2
1
2
1
0
PITCNT Register
0001
0000
00
0001
0000
8-Bit Force Load
2
1
0
2
1
0
PTF Flag
1
PITTRIG
16-Bit Force Load
0001
0000
0001
2
Time-Out Period
Time-Out Period
After Restart
Timer Counter
Note 1. The PTF flag clearing depends on the software
Because
of
an
order
from
the
United
States
International
Trade
Commission,
BGA-packaged
product
lines
and
part
numbers
indicated
here
currently
are
not
available
from
Freescale
for
import
or
sale
in
the
United
States
prior
to
September
2010:
S12XE
products
in
208
MAPBGA
packages
