M68HC16 Z SERIES
SYSTEM INTEGRATION MODULE
USER’S MANUAL
5-39
Figure 5-13 Write Cycle Flowchart
5.6.3 Fast Termination Cycles
When an external device can meet fast access timing, an internal chip-select circuit
fast termination option can provide a two-cycle external bus transfer. Because the
chip-select circuits are driven from the system clock, the bus cycle termination is in-
herently synchronized with the system clock.
If multiple chip-selects are to be used to provide control signals to a single device and
match conditions occur simultaneously, all MODE, STRB, and associated DSACK
fields must be programmed to the same value. This prevents a conflict on the internal
bus when the wait states are loaded into the DSACK counter shared by all chip-se-
lects.
WR CYC FLOW
MCU
PERIPHERAL
ADDRESS DEVICE (S0)
1) DECODE ADDRESS
2) LATCH DATA FROM DATA BUS
ACCEPT DATA (S2 + S3)
3) ASSERT DSACK SIGNALS
TERMINATE CYCLE
NEGATE DSACK
1) SET R/W TO WRITE
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
TERMINATE OUTPUT TRANSFER (S5)
START NEXT CYCLE
ASSERT AS (S1)
PLACE DATA ON DATA[15:0] (S2)
ASSERT DS AND WAIT FOR DSACK (S3)
OPTIONAL STATE (S4)
NO CHANGE
F
re
e
sc
a
le
S
e
m
ic
o
n
d
u
c
to
r,
I
Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
n
c
.
..