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2- 4
MC68349 USER'S MANUAL
MOTOROLA
Table 2-1. Signal Index (Concluded)
Signal Name
Mnemonic
Function
Input/
Output
Request-to-Send A/OP0,
Request-to-Send B/OP1
RTSA , RTSB/
Channel request-to-send outputs or discrete
outputs
Out/Out
Clear-to-Send
CTSA , CTSB
Serial module clear-to-send inputs
In
Synchronizer Power
V
CCSYN
Quiet power supply to VCO; also used to control
synthesizer mode after reset.
—
System Power Supply and
Ground
VCC, GND
Power supply and ground to the MC68349
—
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 MC68349 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.