MC68HC12 MOTOROLA [Motorola, Inc], MC68HC12 Datasheet - Page 110

• Manufacturer Part Number: MC68HC12
• Description: The MC68HC912DT128A microcontroller unit (MCU) is a 16-bit device composed of standard on-chip peripherals including a 16-bit central processing unit
• Manufacturer: MOTOROLA [Motorola, Inc]

Bus Control and Input/Output
Technical Data
110
LSTRE — Low Strobe (LSTRB) Enable
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 or normal
expanded narrow mode.
LSTRB is used during external writes. After reset in normal expanded
mode, LSTRB is disabled. If needed, it should be enabled before
external writes. External reads do not normally need LSTRB because
all 16 data bits can be driven even if the MCU only needs 8 bits of
data.
TAGLO is a shared function of the PE3/LSTRB pin. In special
expanded modes with LSTRE set and the BDM tagging on, a zero at
the falling edge of E tags the instruction word low byte being read into
the instruction queue.
Normal: write once; Special: write anytime EXCEPT the first time.
Read anytime. This bit has no effect in single-chip modes.
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.
0 = PE4 is the external E-clock pin subject to the following
1 = PE4 is a general-purpose I/O pin.
0 = PE3 is a general-purpose I/O pin.
1 = PE3 is configured as the LSTRB bus-control output, provided
0 = PE2 is a general-purpose I/O pin.
1 = PE2 is configured as the R/W pin. In single chip modes, RDWE
limitation: In single-chip modes, to get an E clock output signal,
it is necessary to have ESTR = 0 in addition to NECLK = 0. A
16-bit write to PEAR and MODE registers can configure all
three bits in one operation.
the MCU is not in single chip or normal expanded narrow
modes.
has no effect and PE2 is a general-purpose I/O pin.
Bus Control and Input/Output
MC68HC912DT128A — Rev 4.0
MOTOROLA