Long-Word And Word Read And Write Timing—16-Bit Port - Motorola MC68340 User Manual

S0 S2 S4
CLKOUT
A31–A0
FC3–FC0
R/W
AS
DS
SIZ0
4 BYTES
SIZ1
DSACK0
DSACK1
OP0
D15–D8
OP1
D7–D0
LONG WORD READ
FROM 16-BIT BUS
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.
MOTOROLA
Freescale Semiconductor, Inc.
S0 S2 S4 S0 S2
2 BYTES
2 BYTES
OP2
OP3
WORD READ
FROM 16-BIT BUS
MC68340 USER'S MANUAL
For More Information On This Product,
Go to: www.freescale.com
S4 S0 S2 S4 S0
4 BYTES
OP0
OP0
OP1
OP1
LONG WORD WRITE TO
16-BIT BUS
S4
S2 S4 S0 S2
2 BYTES 2 BYTES
OP2 OP0
OP3 OP1
WORD
WRITE TO
16-BIT BUS
3- 13