Typewriter User Manual

MOTOROLA MC68340 USER’S MANUAL 3- 9
3.2.3.3 BYTE OPERAND TO 16-BIT PORT, ODD (A0 = 1). The MC68340 drives the
address bus with the desired address and the SIZx pins to indicate a single-byte operand.
DSACK0DSACK1A0SIZ0SIZ1
0110X
D0D8D15 D7
(OP0) OP0
OP0
7
0
BYTE OPERAND
DATA BUS
CYCLE 1
For a read operation, the slave responds by placing data on bits 7–0 of the data bus and
asserting
DSACK1 to indicate a 16-bit port. The MC68340 then reads the operand byte
from bits 7–0 and ignores bits 15–8.
For a write operation, the MC68340 drives the single-byte operand on both bytes of the
data bus because it does not know the port size until the
DSACK≈ signals are read. The
slave device reads the operand from bits 7–0 of the data bus and uses the address to
place the operand in the specified location. The slave then asserts
DSACK1 to terminate
the bus cycle.
3.2.3.4 WORD OPERAND TO 8-BIT PORT, ALIGNED. The MC68340 drives the address
bus with the desired address and the SIZx pins to indicate a word operand.
D0D8D15 D7
OP0
OP1
OP0 OP1
15 7 0
DSACK0DSACK1A0SIZ0SIZ1
10010
01110
WORD OPERAND
DATA BUS
CYCLE 1
CYCLE 2
(OP1)
(OP1)
8
For a read operation, 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
MC68340 reads the most significant byte of the operand from bits 15–8 and ignores bits
7–0. The MC68340 then decrements the transfer size counter, increments the address,
and reads the least significant byte of the operand from bits 15–8 of the data bus.
For a write operation, the MC68340 drives the word operand on bits 15–0 of the data bus.
The slave device then reads the most significant byte of the operand from bits 15–8 of the
data bus and asserts
DSACK0 to indicate that it received the data but is an 8-bit port.
The MC68340 then decrements the transfer size counter, increments the address, and
writes the least significant byte of the operand to bits 15–8 of the data bus.
Frees
cale Semiconductor,
I
Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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