MC912DG128A Motorola, MC912DG128A Datasheet - Page 37

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

Single-Wire
Background Mode
Pin (BKGD)
External Address
and Data Buses
(ADDR[15:0] and
DATA[15:0])
Read/Write (R/W)
Low-Byte Strobe
(LSTRB)
11-pins
MOTOROLA
The BKGD pin receives and transmits serial background debugging
commands. A special self-timing protocol is used. The BKGD pin has an
active pullup when configured as an input; BKGD has no pullup control.
Refer to
External bus pins share functions with general-purpose I/O ports A and
B. In single-chip operating modes, the pins can be used for I/O; in
expanded modes, the pins are used for the external buses.
In expanded wide mode, ports A and B are used for multiplexed 16-bit
data and address buses. PA[7:0] correspond to
ADDR[15:8]/DATA[15:8]; PB[7:0] correspond to ADDR[7:0]/DATA[7:0].
In expanded narrow mode, ports A and B are used for the16-bit address
bus, and an 8-bit data bus is multiplexed with the most significant half of
the address bus on port A. In this mode, 16-bit data is handled as two
back-to-back bus cycles, one for the high byte followed by one for the
low byte. PA[7:0] correspond to ADDR[15:8] and to DATA[15:8] or
DATA[7:0], depending on the bus cycle. The state of the address pins
should be latched at the rising edge of E. To allow for maximum address
setup time at external devices, a transparent latch should be used.
In all modes this pin can be used as a general-purpose I/O and is an
input with an active pull-up out of reset. If the read/write function is
required it should be enabled by setting the RDWE bit in the PEAR
register. External writes will not be possible until enabled.
In all modes this pin can be used as a general-purpose I/O and is an
input with an active pull-up out of reset. If the strobe function is required,
it should be enabled by setting the LSTRE bit in the PEAR register. This
signal is used in write operations. Therefore external low byte writes will
not be possible until this function is enabled. This pin is also used as
TAGLO in Special Expanded modes and is multiplexed with the LSTRB
function.
Development
Pinout and Signal Descriptions
Support.
Pinout and Signal Descriptions
MC68HC912DT128A Rev 2.0
Signal Descriptions
37