System Configuration and Protection
MPC561/MPC563 Reference Manual, Rev. 1.2
6-40
Freescale Semiconductor
6.2.2.4
System Timer Registers
The following sections describe registers associated with the system timers. These facilities are powered
by the KAPWR and can preserve their value when the main power supply is off. Refer to
,” for details on the required actions needed in order to guarantee this data retention.
A list of KAPWR registers affected by the key/lock mechanism is found in
.
6.2.2.4.1
Decrementer Register (DEC)
The 32-bit decrementer register is defined by the PowerPC architecture. The values stored in this register
are used by a down counter to cause decrementer exceptions. The decrementer causes an exception
whenever bit zero changes from a logic zero to a logic one. A read of this register always returns the current
count value from the down counter.
Contents of this register can be read or written to by the mfspr or the mtspr instruction. The decrementer
register is reset by PORESET. HRESET and SRESET do not affect this register. The decrementer is
powered by standby power and can continue to count when standby power is applied.
Decrementer counts down the time base clock and the counting is enabled by TBE bit in TBCSR register
Section 6.2.2.4.4, “Time Base Control and Status Register (TBSCR)
.”
Refer to
Section 3.9.5, “Decrementer Register (DEC)
” for more information on this register.
6.2.2.4.2
Time Base SPRs (TB)
The TB is a 64-bit register containing a 64-bit integer that is incremented periodically. There is no
automatic initialization of the TB; the system software must perform this initialization. The contents of the
20:25
—
Reserved
26
DEXT
Data external transfer error acknowledge. This bit is set if the cycle was terminated by an
externally generated TEA signal when a data load or store is requested by an internal master.
27
DBM
Data transfer monitor time out. This bit is set if the cycle was terminated by a bus monitor time-out
when a data load or store is requested by an internal master.
28:31
—
Reserved
MSB
0
LSB
31
Field
DECREMENTING COUNTER
PORESET
0000_0000_0000_0000_0000_0000_0000_0000
HRESET
SRESET
Unaffected
Addr
SPR 22
Figure 6-29. Decrementer Register (DEC)
Table 6-17. TESR Bit Descriptions (continued)
Bits
Name
Description
Summary of Contents for MPC561
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