![](http://datasheet.mmic.net.cn/90000/MC68330FC16_datasheet_3506366/MC68330FC16_38.png)
3- 10
MC68330 USER’S MANUAL
MOTOROLA
For a read operation, the slave responds by placing the data on bits 15-0 of the data bus
and asserting
DSACK1 to indicate a 16-bit port. When DSACK1 is asserted, the MC68330
reads the data on the data bus and terminates the cycle.
For a write operation, the MC68330 asserts
UWE and LWE, and drives the word operand
on bits 15-0 of the data bus. The slave device then reads the entire operand from bits 15-0
of the data bus and asserts
DSACK1 to terminate the bus cycle.
3.2.3.6 LONG-WORD OPERAND TO 8-BIT PORT, ALIGNED. The MC68330 drives the
address bus with the desired address and the size pins to indicate a long-word operand.
DSACK
A0
SIZ0
SIZ
D0
D8
D15
D7
LONG-WORD OPERAN
DATA BU
11110
10010
01110
00010
OP1
OP0
OP2
OP3
31
23
15
7
0
OP0
OP1
OP2
OP3
(OP1
(OP3
CYCLE
For a read operation, shown in Figure 3-3, the slave responds by placing the most
significant byte of the operand on bits 15-8 of the data bus and asserting
DSACK0 to
indicate an 8-bit port. The MC68330 reads the most significant byte of the operand (byte
0) from bits 15-8 and ignores bits 7-0. The MC68330 then decrements the transfer size
counter, increments the address, initiates a new cycle, and reads byte 1 of the operand
from bits 15-8 of the data bus. The MC68330 repeats the process of decrementing the
transfer size counter, incrementing the address, initiating a new cycle, and reading a byte
to transfer the remaining two bytes.
For a write operation, shown in Figure 3-4, the MC68330 drives the two most significant
bytes of the operand on bits 15-0 of the data bus. The slave device then reads only the
most significant byte of the operand (byte 0) from bits 15-8 of the data bus and asserts
DSACK0 to indicate reception and an 8-bit port. The MC68330 then decrements the
transfer size counter, increments the address, and writes byte 1 of the operand to bits 15-
8 of the data bus. The MC68330 continues to decrement the transfer size counter,
increment the address, and write a byte to transfer the remaining two bytes to the slave
device.