MSC8144E Reference Manual, Rev. 3
21-4
Freescale
Semiconductor
Timers
21.1.3.1
Operation of the Cascaded Timer
If the first timer in a cascaded chain is counting up and it encounters a compare event, the timer
connected to it is incremented. If the first timer in the chain is counting down and it encounters a
compare event, the timer is decremented. You can correctly read all 16-bit portions of a cascaded
timer as follows using the TMRxHOLD registers:
1.
Read any 16-bit portion of the cascaded timer from its TMRxCNTR register. You can
do this at any time.
2.
When any TMRxCNTR register in the module is read, all other timers simultaneously
load their values into their hold registers.
3.
Read the 16-bit portions of all other timers in the cascade from their TMRxHOLD
registers.
21.1.3.2
Cascading Restrictions
To ensure that there are no feedback loops in a cascade, there are restrictions on which timers can
be cascaded. The timer with the lowest number must always be the first in the cascade, the timer
with the second lowest number must be second, and so on. The timer with the highest number
must always be last in the cascade. Table 21-2 summarizes the cascading restrictions.
Table 21-2. Restrictions On Cascading Timers
Timer Number
Valid Cascade
Inputs
Legal Values for
Cascading using
TMRxCTL[PCS]
Description
Timer 0
None
None
Timer 0 can only be the first timer in a cascaded timer. It
cannot receive another timer’s output for cascaded operation.
Timer 0 must always be the first timer in the cascade.
Timer 1
Timer 0 output
0100: Timer 0
Timer 1 can be cascaded with Timer 0, with Timer 0 as the
first timer in the chain.
Timer 2
Timer 0 output
Timer 1 output
0100: Timer 0
0101: Timer 1
Timer 2 can be cascaded with Timer 0 or Timer 1 when Timer
2 is not the first timer in the cascade.
Timer 3
Timer 0 output
Timer 1 output
Timer 2 output
0100: Timer 0
0101: Timer 1
0110: Timer 2
Timer 3 can be cascaded with Timer 0, Timer 1, or Timer 3.
Timer 3 must always be the last timer in a cascade.
Summary of Contents for MSC8144E
Page 1: ...MSC8144E Reference Manual Quad Core Media Signal Processor MSC8144ERM Rev 3 July 2009 ...
Page 48: ...MSC8144E Reference Manual Rev 3 xlviii Freescale Semiconductor ...
Page 86: ...MSC8144E Reference Manual Rev 3 1 38 Freescale Semiconductor Overview ...
Page 168: ...MSC8144E Reference Manual Rev 3 3 60 Freescale Semiconductor External Signals ...
Page 242: ...MSC8144E Reference Manual Rev 3 5 26 Freescale Semiconductor Reset ...
Page 314: ...MSC8144E Reference Manual Rev 3 8 24 Freescale Semiconductor General Configuration Registers ...
Page 414: ...MSC8144E Reference Manual Rev 3 10 14 Freescale Semiconductor MSC8144E SC3400 DSP Subsystem ...
Page 452: ...MSC8144E Reference Manual Rev 3 11 38 Freescale Semiconductor Internal Memory Subsystem ...
Page 520: ...MSC8144E Reference Manual Rev 3 12 68 Freescale Semiconductor DDR SDRAM Memory Controller ...
Page 1070: ...MSC8144E Reference Manual Rev 3 21 28 Freescale Semiconductor Timers ...