MPC5553/MPC5554 Microcontroller Reference Manual, Rev. 5
Freescale Semiconductor
11-21
11.4.1.3
Clock Dividers
Each of the CLKOUT, MCKO, and ENGCLK dividers provides a nominal 50% duty cycle clock to an
output pin. There is no guaranteed phase relationship between CLKOUT, MCKO, and ENGCLK.
ENGCLK is not synchronized to any I/O pins.
11.4.1.3.1
External Bus Clock (CLKOUT)
The external bus clock (CLKOUT) divider can be programmed to divide the system clock by two or four
based on the settings of the EBDF bit field in the SIU external clock control register (SIU_ECCR). The
reset value of the EBDF selects a CLKOUT frequency of one half of the system clock frequency. The EBI
supports gating of the CLKOUT signal when there are no external bus accesses in progress. See the
Chapter 6, “System Integration Unit (SIU)
” for more information on CLKOUT.
The hold-time for the external bus pins can be changed by writing to the external bus tap select (EBTS)
bit in the SIU_ECCR. See
Chapter 6, “System Integration Unit (SIU)
11.4.1.3.2
Nexus Message Clock (MCKO)
The Nexus message clock (MCKO) divider can be programmed to divide the system clock by two, four or
eight based on the MCKO_DIV bit field in the port configuration register (PCR) in the Nexus port
controller (NPC). The reset value of the MCKO_DIV selects an MCKO clock frequency one half of the
system clock frequency. The MCKO divider is configured by writing to the NPC through the JTAG port.
See
Chapter 25, “Nexus Development Interface
eTPU Engine A
ETPUECR_1
MDIS
eTPU Engine B
ETPUECR_2
MDIS
FlexCAN A
FLEXCAN_A_MCR
MDIS
FlexCAN B
1
FLEXCAN_B_MCR
MDIS
FlexCAN C
FLEXCAN_C_MCR
MDIS
EMIOS
EMIOS_MCR
MDIS
ESCI_A
ESCIA_CR2
MDIS
ESCI_B
ESCIB_CR2
MDIS
NPC
NPC_PCR
MCKO_EN, MCKO_GT
2
Flash Array
FLASH_MCR
STOP
3
1
Shaded areas indicate that module is only offered on the MPC5554, not on the
MPC5553.
2
See
Chapter 25, “Nexus Development Interface
.”
3
See
.”
Table 11-7. Software Controlled Power Management/Clock Gating Support (Continued)
Module Name
Register Name
Bit Names
Summary of Contents for MPC5553
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