Freescale Semiconductor, Inc.
Bus Control and Input/Output
Registers
In normal expanded modes, the reset vector is located in external
memory. The DBE and E clock are required for de-multiplexing address
and data, but LSTRB and R/W are only needed by the system when
there are external writable resources. Therefore in normal expanded
modes, only the DBE and E clock are configured for their alternate bus
control functions and the other bits of port E are configured for general-
purpose I/O. If the normal expanded system needs any other bus-control
signals, PEAR would need to be written before any access that needed
the additional signals.
In special expanded modes, DBE, IPIPE1, IPIPE0, E, LSTRB, and R/W
are configured as bus-control signals.
In peripheral mode, the PEAR register is not accessible for reads or
writes. However, the CGMTE control bit is reset to one to configure PE6
as a test output from the PLL module.
NDBE — No Data Bus Enable
Normal: write once; Special: write anytime EXCEPT the first. Read
anytime.
0 = PE7 is used for DBE, external control of data enable on
memories, or inverted E clock.
1 = PE7 is the CAL function if CALE bit is set in PEAR register or
general-purpose I/O.
NDBE controls the use of the DBE pin of Port E. The NDBE bit has no
effect in Single Chip or Peripheral Modes. The associated pin will
default to the CAL function if the CALE bit is set in PEAR register or
otherwise to an I/O.
CGMTE — Clock Generator Module Testing Enable
Normal: write never; Special: write anytime EXCEPT the first. Read
anytime.
0 = PE6 is general-purpose I/O or pipe output.
1 = PE6 is a test signal output from the CGM module (no effect in
single chip or normal expanded modes). PIPOE = 1 overrides
this function and forces PE6 to be a pipe status output signal.
68HC(9)12D60 — Rev 4.0
MOTOROLA
Advance Information
Bus Control and Input/Output
93
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