MC912DG128A Motorola, MC912DG128A Datasheet - Page 88

• Manufacturer Part Number: MC912DG128A
• Description: Microcontrollers
• Manufacturer: Motorola

Bus Control and Input/Output
MC68HC912DT128A Rev 2.0
88
NDBE — No Data Bus Enable
CGMTE — Clock Generator Module Testing Enable
The reset condition of this register depends on the mode of operation
because bus control signals are needed immediately after reset in
some modes.
In normal single-chip mode, no external bus control signals are
needed so all of port E is configured for general-purpose I/O.
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, the DBE and the 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 special single chip modes, DBE, IPIPE1, IPIPE0, E, LSTRB, R/W,
and CALE 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 for the CGM module.
Normal: write once; Special: write anytime EXCEPT the first. Read
anytime.
The NDBE bit has no effect in Single Chip or Peripheral Modes and
PE7 is defaulted to the CAL function if CALE bit is set in PEAR
register or to an I/O otherwise.
Normal: write never; Special: write anytime EXCEPT the first time.
Read anytime.
0 = PE7 is used for DBE, external control of data enable on
1 = PE7 is CAL function if CALE bit is set in PEAR register or
0 = PE6 is general-purpose I/O or pipe output.
memories, or inverted E clock.
general-purpose I/O otherwise.
Bus Control and Input/Output
MOTOROLA
6-bus