Freescale Semiconductor, Inc.
Bus Control and Input/Output
Registers
RDWE — Read/Write Enable
Normal: write once; Special: write anytime EXCEPT the first time.
Read anytime. This bit has no effect in single-chip modes.
0 = PE2 is a general-purpose I/O pin.
1 = PE2 is configured as the R/W pin. In single chip modes, RDWE
has no effect and PE2 is a general-purpose I/O pin.
R/W is used for external writes. After reset in normal expanded mode,
it is disabled. If needed it should be enabled before any external
writes.
CALE — Calibration Reference Enable
Read and write anytime.
0 = Calibration reference is disabled and PE7 is general-purpose
I/O in single chip or peripheral modes or if the NDBE bit is set.
1 = Calibration reference is enabled on PE7 in single chip and
peripheral modes or if the NDBE bit is set.
DBENE — DBE or Inverted E Clock on Port E[7]
Normal modes: write once. Special modes: write anytime EXCEPT
the first; read anytime.
DBENE controls which signal is output on PE7 when NDBE control bit
is cleared. The inverted E clock output can be used to latch the
address for demultiplexing. It has the same behaviour as the E clock,
except it is inverted. Please note that in the case of idle expansion
bus, the ‘not E clock’ signal could stay high for many cycles.
The DBNE bit has no effect in single chip or peripheral modes and
PE7 is defaulted to the CAL function if the CALE bit is set in the PEAR
register or to an I/O otherwise.
0 = PE7 pin used for DBE external control of data enable on
memories in expanded modes when NDBE = 0
1 = PE7 pin used for inverted E clock output in expanded modes
when NDBE = 0
68HC(9)12D60 — Rev 4.0
MOTOROLA
Advance Information
Bus Control and Input/Output
95
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