System Interface Unit
MPC885 PowerQUICC Family Reference Manual, Rev. 2
10-26
Freescale Semiconductor
and the count resumes with a new value in the PITC. If the PTE bit is not set, the PIT is unable to count
and retains the old count value. Reading the PIT does not affect it.
Figure 10-23. Periodic Interrupt Timer Block Diagram
The time-out period is calculated as follows:
10.10.1 Periodic Interrupt Status and Control Register (PISCR)
The periodic interrupt status and control register (PISCR), shown in
Figure 10-24
, contains the interrupt
request level and status bits. It also controls the 16 bits to be loaded in a modulus counter. Note that PISCR
is a keyed register. It must be unlocked in PISCRK before it can be written.
This register is affected by HRESET but is not affected by SRESET.
Table 10-20
describes PISCR fields.
0
7
8
9
12
13
14
15
Field
PIRQ
PS
—
PIE
PITF
PTE
Reset
0000_0000_0000_0000
R/W
R/W
Addr
(IMMR & 0xFFFF0000) + 0x240
Figure 10-24. Periodic Interrupt Status and Control Register (PISCR)
Table 10-20. PISCR Field Descriptions
Bits
Name
Description
0–7
PIRQ
Periodic interrupt request level. Configures internal interrupt levels for periodic interrupts.
Figure 10-7
shows interrupt request levels.
8
PS
Periodic interrupt status. Can be cleared by writing a 1 to it (zero has no effect).
0 The PIT is unaffected.
1 The PIT has issued an interrupt.
9–12
—
Reserved, should be cleared.
Clock
Disable
PIT
Interrupt
PITCLK
Clock
16-Bit
Modulus Counter
PTE
PITC
PS
PIE
FRZ
PITperiod
PITC 1
+
Fpitclk
-------------------------
PITC 1
+
ExternalClock
1
o
or
o
128
------------------------------------------
⎝
⎠
⎛
⎞
4
÷
------------------------------------------------------------
=
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Summary of Contents for PowerQUICC MPC870
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Page 1090: ...UTOPIA Interface MPC885 PowerQUICC Family Reference Manual Rev 2 43 8 Freescale Semiconductor ...
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