Typewriter User Manual

MOTOROLA MC68340 USER’S MANUAL 3- 13
CLKOUT
A31–A0
FC3–FC0
SIZ0
SIZ1
D15–D8
D7–D0
R/W
AS
DS
DSACK0
DSACK1
2 BYTES
2 BYTES
4 BYTES
S0 S2 S4 S0 S2 S4 S0 S2 S4 S0 S2 S4 S0 S2 S4 S0 S2
S4
2 BYTES 2 BYTES
OP0
OP1
OP2
OP3
OP0
OP1
OP0
OP2
OP0
OP1OP3
OP1
WORD READ
FROM 16-BIT BUS
LONG WORD WRITE TO
16-BIT BUS
WORD
WRITE TO
16-BIT BUS
LONG WORD READ
FROM 16-BIT BUS
4 BYTES
Figure 3-5. Long-Word and Word Read and Write Timing—16-Bit Port
The MC68340 drives the address bus with the desired address and drives the SIZx pins to
indicate a long-word operand. For a read operation, the slave responds by placing the two
most significant bytes of the operand on bits 15–0 of the data bus and asserting
DSACK1
to indicate a 16-bit port. The MC68340 reads the two most significant bytes of the operand
(bytes 0 and 1) from bits 15–0. The MC68340 then decrements the transfer size counter
by 2, increments the address by 2, initiates a new cycle, and reads bytes 2 and 3 of the
operand from bits 15–0 of the data bus.
For a write operation, the MC68340 drives the two most significant bytes of the operand
on bits 15–0 of the data bus. The slave device then reads the two most significant bytes of
the operand (bytes 0 and 1) from bits 15–0 of the data bus and asserts
DSACK1 to
indicate reception and a 16-bit port. The MC68340 then decrements the transfer size
counter by 2, increments the address by 2, and writes bytes 2 and 3 of the operand to bits
15–0 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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