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MPC555
/
MPC556
TIME PROCESSOR UNIT 3
MOTOROLA
USER’S MANUAL
Rev. 15 October 2000
17-5
TPU function library. Refer to the Motorola
TPU Literature Package (TPULITPAK/D)
for more information about specific functions.
17.3.7 TPU3 Interrupts
Each of the TPU3 channels can generate an interrupt service request. Interrupts for
each channel must be enabled by writing to the appropriate control bit in the channel
interrupt enable register (CIER). The channel interrupt status register (CISR) contains
one interrupt status flag per channel. Time functions set the flags. Setting a flag bit
causes the TPU3 to make an interrupt service request if the corresponding channel
interrupt enable bit is set.
The TPU3 can generate one of 32 possible interrupt request levels on the IMB3. The
value driven onto IRQ[7:0] represents the interrupt level programmed in the IRL field
of the TPU interrupt configuration register (TICR). Under the control of the ILBS bits in
the ICR, each interrupt request level is driven during the time multiplexed bus during
one of four different time slots, with eight levels communicated per time slot. No hard-
ware priority is assigned to interrupts. Furthermore, if more than one source on a mod-
ule requests an interrupt at the same level, the system software must assign a priority
to each source requesting at that level.
displays the interrupt level
scheme.
Figure 17-2 TPU3 Interrupt Levels
17.3.8 Prescaler Control for TCR1
Timer count register 1 (TCR1) is clocked from the output of a prescaler. The following
fields control TCR1:
• The PSCK and TCR1P fields in TPUMCR
• The DIV2 field in TPUMCR2
• The EPSCKE and EPSCK fields in TPUMCR3.
The rate at which TCR1 is incremented is determined as follows:
• The user selects either the standard prescaler (by clearing the enhanced prescal-
er enable bit, EPSCKE, in TPUMCR3) or the enhanced prescaler (by setting
EPSCKE).
IMB3 CLOCK
ILBS[1:0]
IMB3 IRQ[7:0]
IRQ
7:0
00
01
11
10
IRQ
15:8
IRQ
23:16
IRQ
31:24
IRQ
7:0
00
01
11
10
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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