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MC68341 USER’S MANUAL
MOTOROLA
2.2.1 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 MC68341 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.
2.2.1.1 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.
2.2.1.2 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 MC68341 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.
2.2.2 Address Strobe (
AS)
AS is an output timing signal for MC68300 cycles that indicates the validity of both an
address on the address bus and many control signals. AS is asserted approximately one-
half clock cycle after the beginning of a bus cycle.
2.2.3 M68000 Address Strobe (
AS68K)
AS68K is an output timing signal for MC68000 cycles that indicates that the information on
the address bus is a valid address.
2.2.4 Data Bus (D15–D0)
This bidirectional, nonmultiplexed, parallel bus contains the data being transferred to or
from the MC68341. 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 MC68341 on the
last falling edge of the clock for that bus cycle. For a write cycle, all 16 bits of the data bus
are driven, regardless of the port width or operand size. The MC68341 places the data on
the data bus approximately one-half clock cycle after AS is asserted in a write cycle.
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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