mcf5272 Freescale Semiconductor, Inc, mcf5272 Datasheet - Page 308

• Manufacturer Part Number: mcf5272
• Description: Mcf5272 Coldfire Integrated Microprocessor User
• Manufacturer: Freescale Semiconductor, Inc

PLIC Timing Generator
The clock generator uses a 14-bit counter to divide CLKIN. This limits the reference
clock’s minimum frequency to CLKIN divided by 16,384.
To summarize these two points:
The control of the clock generator block is provided through the PCSR register detailed in
Section 13.5.22, “Clock Select Register (PCSR).”
The process is illustrated by this example. Suppose the following:
The appropriate reference clock is selected by programming PLCLKSEL[CKI1, CKI0],
Section 13.5.22, “Clock Select Register (PCSR).” The multiplication factor is 16
(1.024 MHz / 64 KHz) and is specified by PLCLKSEL[CMULT0-2]. The division ratio
between the synthesized clock (GDCL), 1.024 MHz, and the synthesized frame sync
(Gen_FSC) must be set. (A Gen_FSC of 8 KHz is assumed). This division ratio is selected
by means of FDIV[2-0]. Finally, the clock generation block should be taken out of bypass
by setting PCSR[NBP].
The above settings can be made by a single write of the 16-bit value 0x802B to PCSR.
The following restrictions should be observed when using the clock generator module:
Figure 13-11 and Figure 13-12 show the connectivity and relationship of the timing signals
within the PLIC block.
13.3.2 Super Frame Sync Generation
Figure 13-11 shows the generation of the 2-KHz super frame sync. The choice of either
FSC0 or FSC1 is possible using P1CR[FSM]. This allows either the port 0 or port 1 timing
to be used to generate the 2-KHz super frame sync interrupt. The SFSC block then divides
this accordingly. When P1CR[FSM] is set, FSC1 is the source of the super frame sync. In
case P1CR[MS] is 0 (that is, port 1 is in slave mode), the interrupt is ultimately driven by
an external source. In case the M/S bit is 1 (that is, port 1 is in master mode), FSC1
ultimately comes from port 0.
13-12
• Synthesized clock x 20 < CLKIN
• Reference clock > CLKIN / 16,384
• CPU clock = 66 MHz
• Reference clock = 64 KHz
• Synthesized clock = 1.024 MHz
• The smallest multiplication factor is 2.
• CLKIN should be significantly greater than (> 20 times) the synthesized clock.
MCF5272 User’s Manual
(Recommended)
(Required)
MOTOROLA