System Configuration and Protection
MPC561/MPC563 Reference Manual, Rev. 1.2
6-18
Freescale Semiconductor
MPC561/MPC563, and RCPU access is terminated with a data error, causing a machine check state or
exception.
The bus monitor timing bit in the system protection control register (SYPCR[BMT]) defines the bus
monitor time-out period. The programmability of the time-out allows for variation in system peripheral
response time. The timing mechanism is clocked by the external bus clock divided by eight. The maximum
value is 2040 system clock cycles.
SYPCR[BME] enables or disables the bus monitor. But regardless of the state of this bit the bus monitor
is always enabled when freeze is asserted in debug mode.
6.1.6
Decrementer (DEC)
The decrementer (DEC) is a 32-bit decrementing counter defined by the MPC561/MPC563 architecture
to provide a decrementer interrupt. This binary counter is clocked by the same frequency as the time base
(also defined by the MPC500 architecture). The operation of the time base and decrementer are therefore
coherent. The DEC is clocked by the TMBCLK clock. The decrementer period is computed as follows:
The state of the DEC is not affected by any resets and should be initialized by software. The DEC runs
continuously after power-up once the time base is enabled by setting the TBE bit of the TBSCR (see
) (unless the clock module is programmed to turn off the clock). The decrementer continues
counting while reset is asserted.
Reading from the decrementer has no effect on the counter value. Writing to the decrementer replaces the
value in the decrementer with the value in the GPR.
Whenever bit 0 (the MSB) of the decrementer changes from zero to one, a decrementer exception occurs.
If software alters the decrementer such that the content of bit 0 is changed to a value of 1, a decrementer
exception occurs.
A decrementer exception causes a decrementer interrupt request to be pending in the RCPU. When the
decrementer exception is taken, the decrementer interrupt request is automatically cleared.
illustrates some of the periods available for the decrementer, assuming a 4-MHz or 20-MHz
crystal, and TBS = 0 which selects TMBCLK division to 4.
NOTE
Time base must be enabled to use the decrementer. See
“Time Base Control and Status Register (TBSCR)
,” for more information.
Table 6-6. Decrementer Time-Out Periods
Count Value
Time-Out @ 4 MHz
Time-Out @ 20 MHz
0
1.0 µs
0.2 µs
9
10 µs
2.0 µs
T
DEC
=
2
32
F
TMBCLK
Summary of Contents for MPC561
Page 84: ...MPC561 MPC563 Reference Manual Rev 1 2 lxxxiv Freescale Semiconductor...
Page 144: ...Signal Descriptions MPC561 MPC563 Reference Manual Rev 1 2 2 46 Freescale Semiconductor...
Page 206: ...Central Processing Unit MPC561 MPC563 Reference Manual Rev 1 2 3 62 Freescale Semiconductor...
Page 302: ...Reset MPC561 MPC563 Reference Manual Rev 1 2 7 14 Freescale Semiconductor...
Page 854: ...Time Processor Unit 3 MPC561 MPC563 Reference Manual Rev 1 2 19 24 Freescale Semiconductor...
Page 968: ...Development Support MPC561 MPC563 Reference Manual Rev 1 2 23 54 Freescale Semiconductor...
Page 1144: ...Internal Memory Map MPC561 MPC563 Reference Manual Rev 1 2 B 34 Freescale Semiconductor...
Page 1212: ...TPU3 ROM Functions MPC561 MPC563 Reference Manual Rev 1 2 D 60 Freescale Semiconductor...
Page 1216: ...Memory Access Timing MPC561 MPC563 Reference Manual Rev 1 2 E 4 Freescale Semiconductor...