2- 2
MC68349 USER'S MANUAL
MOTOROLA
2.1 SIGNAL INDEX
The input and output signals for the MC68349 are listed in Table 2-1. The name,
mnemonic, and brief functional description are presented. For more detail on each signal,
refer to the signal paragraph. Guaranteed timing specifications for the signals listed in
Table 2-1 can be found in Section 11 Electrical Characteristics.
Table 2-1. Signal Index
Signal Name
Mnemonic
Function
Input/
Output
Address Bus Bits 23–0
A23–A0
Lower 24 bits of the address bus
Out
Address Bits 31–24/PortA7–0/
Interrupt Acknowledge 7–1
A31–A24
Upper eight bits of the address bus, parallel I/O,
or interrupt acknowledge lines
Out/I/O/
Out
Data Bus
D31–D0
32-bit data bus used to transfer byte, word,
three-byte, or long-word data
I/O
Function Codes
FC3–FC0
Identify the processor state and the address
space of the current bus cycle
Out
Reset
RESET
System reset
I/O
Bus Error
BERR
Indicates an invalid bus operation is being
attempted
In
Halt
HALT
Suspends external bus activity
I/O
Address Strobe
AS
Indicates that a valid address is on the address
bus
Out
Data Strobe
DS
During a read cycle, DS indicates that an
external device should place valid data on the
data bus. During a write cycle, DS indicates that
valid data is on the data bus.
Out
Read/Write
R/ W
Indicates the direction of data transfer on the bus
Out
Size
SIZ1, SIZ0
Indicates the number of bytes remaining to be
transferred for this cycle
Out
Data and Size Acknowledge
DSACK1, DSACK0
Provides asynchronous data transfers and
dynamic bus sizing
In
Bus Request
BR
Indicates that an external device requires bus
mastership
In
Bus Grant
BG
Indicates that current bus cycle is complete and
the MC68349 has relinquished the bus
Out
Bus Grant Acknowledge
BGACK
Indicates that an external device has assumed
bus mastership
In
Read-Modify-Write Cycle
RMC
Identifies the bus cycle as part of an indivisible
read-modify-write operation
Out
Interrupt Request Levels 7, 6, 5,
3/ PortB7, 6, 5, 3
IRQ7 , IRQ6, IRQ5 ,
IRQ3
Provides an interrupt priority level to the CPU32+
or becomes a parallel I/O port
In/I/O
Chip Select 3–1/Interrupt
Request Levels 4, 2, 1/PortB4,
2, 1
CS3–CS1
Enables peripherals at programmed addresses,
interrupt priority level to the CPU32+, or parallel
I/O port
Out/In/
I/O
Chip Select 0/Autovector
CS0
Enables peripherals at programmed addresses
or requests an automatic vector
Out/In