MC68332
SYSTEM INTEGRATION MODULE
USER’S MANUAL
4-27
When AS, DS, and R/W are valid, a peripheral device either places data on the bus
(read cycle) or latches data from the bus (write cycle). At the appropriate time, chip-
select logic asserts data and size acknowledge signals.
The DSACK option fields in the chip-select option registers determine whether inter-
nally generated DSACK or externally generated DSACK are used. For fast termination
for information about fast-termination setup.
To use fast-termination, an external device must be fast enough to have data ready,
within the specified setup time, by the falling edge of S4. Refer to APPENDIX A ELEC- for tabular information about fast termination timing.
When fast termination is in use, DS is asserted during read cycles but not during write
cycles. The STRB field in the chip-select option register used must be programmed
with the address strobe encoding to assert the chip select signal for a fast-termination
write.
4.5.4 CPU Space Cycles
Function code signals FC[2:0] designate which of eight external address spaces is ac-
cessed during a bus cycle. Address space 7 is designated CPU space. CPU space is
used for control information not normally associated with read or write bus cycles.
for more information on codes and encoding.
During a CPU space access, ADDR[19:16] are encoded to reflect the type of access
being made. Figure 4-11 shows the three encodings used by 68300 family microcon-
trollers. These encodings represent breakpoint acknowledge (Type $0) cycles, low
power stop broadcast (Type $3) cycles, and interrupt acknowledge (Type $F) cycles.
Refer to 4.7 Interrupts for information about interrupt acknowledge bus cycles.
Figure 4-11 CPU Space Address Encoding
CPU SPACE CYC TIM
0000000000000000000
T 0
BKPT#
19
23
16
000000111111111111111110
19
16
23
111
11111111111111111111
1
111
LEVEL
19
16
23
CPU SPACE CYCLES
FUNCTION
CODE
20
0
CPU SPACE
TYPE FIELD
ADDRESS BUS
BREAKPOINT
ACKNOWLEDGE
LOW POWER
STOP BROADCAST
INTERRUPT
ACKNOWLEDGE
2
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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