SPMCK16Z4MPV20 datasheet(144/500 Pages) FREESCALE

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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 5.5.2 Dynamic Bus Sizing and 5.5.4 Misaligned Operands for more infor-

mation. Figure 5-13 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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