MOTOROLA
MC68330 USER’S MANUAL
2- 1
SECTION 2
SIGNAL DESCRIPTIONS
This section contains brief descriptions of the MC68330 input and output signals in their
functional groups as shown in Figure 2-1.
2.1 SIGNAL INDEX
The input and output signals for the MC68330 are listed in Table 2-1. The name,
mnemonic, and brief functional description are presented. For more detail on each signal,
refer to the paragraph named for the signal. Guaranteed timing specifications for the
signals listed in Table 2-1 can be found in
MC68330/D, MC68330 Technical Summary.
2.2 ADDRESS BUS
The address bus consists of the following two groups. Refer to 3.1.3 Address Bus 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. Refer to 3.4 CPU Space Cycles for more
information on the CPU address space. A23 is the most significant address signal in this
group.
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 strobes. These pins can be used for more than one of their
multiplexed functions as long as the external demultiplexing circuit properly resolves
collisions between the different functions.
A31–A24. These pins can function as the most significant eight address bits. A31 is the
most significant address signal in this group.
Port A7–Port A0. These eight pins can serve as a dedicated parallel I/O port. See 4.2.5.1
Port A for more information on programming these pins.
IACK7–IACK1. The MC68330 asserts one of these pins to indicate the level of an
external interrupt during an interrupt acknowledge (IACK) cycle. Peripherals can use the
IACK strobes instead of monitoring the address bus and function codes to determine that
an IACK cycle is in progress and to obtain the current interrupt level. See 3.4.4 Interrupt
Acknowledge Bus Cycles for more information. Only seven of these eight pins are used
as IACK strobe outputs since there is no
IACK0 strobe.