SYSTEM INTEGRATION MODULE
M68HC16 Z SERIES
5-38
USER’S MANUAL
Figure 5-12 Word Read Cycle Flowchart
5.6.2.2 Write Cycle
During a write cycle, the MCU transfers data to an external memory or peripheral de-
vice. If the instruction specifies a long-word or word operation, the MCU attempts to
write two bytes at once. For a byte operation, the MCU writes one byte. The portion of
the data bus upon which each byte is written depends on operand size, peripheral ad-
dress, and peripheral port size.
Refer to
and
for more infor-
mation.
is a flowchart of a write-cycle operation for a word transfer. Refer
to the
SIM Reference Manual (SIMRM/AD) for more information.
RD CYC FLOW
MCU
PERIPHERAL
ADDRESS DEVICE (S0)
1) SET R/W TO READ
2) DRIVE ADDRESS ON ADDR[23:0]
3) DRIVE FUNCTION CODE ON FC[2:0]
4) DRIVE SIZ[1:0] FOR OPERAND SIZE
START NEXT CYCLE (S0)
1) DECODE ADDR, R/W, SIZ[1:0], DS
2) PLACE DATA ON DATA[15:0] OR
DATA[15:8] IF 8-BIT DATA
PRESENT DATA (S2)
3) DRIVE DSACK SIGNALS
TERMINATE CYCLE (S5)
1) REMOVE DATA FROM DATA BUS
2) NEGATE DSACK
ASSERT AS AND DS (S1)
DECODE DSACK (S3)
LATCH DATA (S4)
NEGATE AS AND DS (S5)
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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