M68SDIL datasheet(49/432 Pages) MOTOROLA

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Pinout and Signal Descriptions

Signal Descriptions

68HC(9)12D60 — Rev 4.0

Advance Information

MOTOROLA

Pinout and Signal Descriptions

3.5.8 External Address and Data Buses (ADDR[15:0] and DATA[15:0])

External bus pins share function 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 pin

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.

3.5.9 Read/Write (R/W)

In all modes this pin can be used as 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.

3.5.10 Low-Byte Strobe (LSTRB)

In all modes this pin can be used as 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 and so 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.

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