Typewriter User Manual
2- 4 MC68340 USER’S MANUAL MOTOROLA
NOTE
The terms
assert
and
negate
are used throughout this section
to avoid confusion when dealing with a mixture of active-low
and active-high signals. The term
assert
or
assertion
indicates
that a signal is active or true, independent of the level
represented by a high or low voltage. The term
negate
or
negation
indicates that a signal is inactive or false.
2.2 ADDRESS BUS
The address bus signals are outputs that define the address of the byte (or the most
significant byte) to be transferred during a bus cycle. The MC68340 places the address on
the bus at the beginning of a bus cycle. The address is valid while
AS is asserted.
The address bus consists of the following two groups. Refer to Section 3 Bus Operation
for information on the address bus and its relationship to bus operation.
2.2.1 Address Bus (A23–A0)
These three-state outputs (along with A31–A24) provide the address for the current bus
cycle, except in the CPU address space.
2.2.2 Address Bus (A31–A24)
These pins can be programmed as the most significant eight address bits, port A parallel
I/O, or interrupt acknowledge signals. These pins can be used for more than one of their
multiplexed functions as long as the external demultiplexing circuit properly resolves
interaction between the different functions.
A31–A24
These pins can function as the most significant eight address bits.
Port A7–A0
These eight pins can serve as a dedicated parallel I/O port. See Section 4 System
Integration Module for more information on programming these pins.
IACK7– IACK1
The MC68340 asserts one of these pins to indicate the level of an external interrupt
during an interrupt acknowledge cycle. Peripherals can use the
IACK≈ signals instead
of monitoring the address bus and function codes to determine that an interrupt
acknowledge cycle is in progress and to obtain the current interrupt level.
2.3 DATA BUS (D15–D0)
This bidirectional, nonmultiplexed, parallel bus contains the data being transferred to or
from the MC68340. A read or write operation may transfer 8 or 16 bits of data (one or two
bytes) in one bus cycle. During a read cycle, the data is latched by the MC68340 on the
Frees
cale Semiconductor,
I
Freescale Semiconductor, Inc.
For More Information On This Product,
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