mpc823rg Freescale Semiconductor, Inc, mpc823rg Datasheet - Page 281

• Manufacturer Part Number: mpc823rg
• Description: Mpc823 Powerquicc Integrated Communications Processor For Portable Systems
• Manufacturer: Freescale Semiconductor, Inc

System Interface Unit
12.5 THE POWERPC DECREMENTER
The 32-bit decrementing counter is defined by the PowerPC architecture to provide a
decrementer interrupt. This binary counter is clocked by the same frequency as the
timebase. In the MPC823, the decrementer is clocked by the TMBCLK clock, so you must
enable the TBE bit in the TBSCR for the decrementer to start.
The state of the decrementer is not affected by HRESET and SRESET and, therefore, must
be initialized by the software. The decrementer runs continuously after power-up. It
continues counting while HRESET and SRESET are asserted and it is implemented with the
following requirements in mind. The decrementer interrupt is also sent to the power-down
wake-up logic, which allows the CPU to be awaken from power-down mode.
A decrementer exception causes a pending decrementer interrupt request in the core. When
the decrementer interrupt is taken, the request is automatically cleared. The following chart
shows some of the periods available for the decrementer, assuming that a 4MHz oscillator
is used.
• The operation of the timebase and decrementer are coherent, which means the
• The decrementer is unaffected when read.
• When storing to the decrementer, the value in the decrementer is replaced with the
• When Bit 0 (MSB) of the decrementer changes from 0 to 1, an interrupt request is
• If the decrementer is altered by the software and the content of Bit 0 is changed from
COUNT VALUE
T dec
counters are driven by the same fundamental timebase.
value in the GPR.
signaled. If multiple decrementer interrupt requests are received before the first one is
reported, only one interrupt is reported.
0 to 1, an interrupt request is signaled.
0
9
99
999
9999
=
---------------------------- -
F tmbclk
2
32
Freescale Semiconductor, Inc.
100. microseconds
For More Information On This Product,
10. microseconds
10.0 milliseconds
1.0 millisecond
1 microsecond
TIMEOUT
MPC823 REFERENCE MANUAL
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COUNT VALUE
FFFFFFFF(hex)
999999
9999999
99999999
999999999
100.0 seconds
1000. seconds
4295 seconds
10.0 seconds
1.0 second
TIMEOUT
MOTOROLA