mc68331cpv20b1 Freescale Semiconductor, Inc, mc68331cpv20b1 Datasheet - Page 67

• Manufacturer Part Number: mc68331cpv20b1
• Description: Mc68331 32 Bit Microcontroller
• Manufacturer: Freescale Semiconductor, Inc

4.5.2.2 Write Cycle
4.5.3 Fast Termination Cycles
MC68331
USER’S MANUAL
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 4.4.2 Dynamic Bus Sizing and 4.4.4 Misaligned Operands for more infor-
mation. Figure 4-10 is a flowchart of a write-cycle operation for a word transfer. Refer
to the SIM Reference Manual (SIMRM/AD) for more information.
When an external device has a fast access time, the chip-select circuit fast-termination
option can provide a two-cycle external bus transfer. Because the chip-select circuits
2) DRIVE ADDRESS ON ADDR[23:0]
3) DRIVE FUNCTION CODE ON FC[2:0]
4) DRIVE SIZ[1:0] FOR OPERAND SIZE
1) NEGATE DS AND AS
2) REMOVE DATA FROM DATA BUS
1) SET R/W TO WRITE
ASSERT DS AND WAIT FOR DSACK (S3)
TERMINATE OUTPUT TRANSFER (S5)
PLACE DATA ON DATA[15:0] (S2)
ADDRESS DEVICE (S0)
OPTIONAL STATE (S4)
START NEXT CYCLE
ASSERT AS (S1)
NO CHANGE
MCU
Freescale Semiconductor, Inc.
For More Information On This Product,
Figure 4-10 Write Cycle Flowchart
SYSTEM INTEGRATION MODULE
Go to: www.freescale.com
1) DECODE ADDRESS
2) LATCH DATA FROM DATA BUS
3) ASSERT DSACK SIGNALS
1) NEGATE DSACK
ACCEPT DATA (S2 + S3)
TERMINATE CYCLE
PERIPHERAL
WR CYC FLOW
4-25
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