SYSTEM INTEGRATION MODULE MC68332
4-56 USER’S MANUAL
During a CPU space cycle, bits [15:3] of the appropriate base register must be config-
ured to match ADDR[23:11], as the address is compared to an address generated by
the CPU.
Figure 4-19 shows CPU space encoding for an interrupt acknowledge cycle. FC[2:0]
are set to %111, designating CPU space access. ADDR[3:1] indicate interrupt priority,
and the space type field (ADDR[19:16]) is set to %1111, the interrupt acknowledge
code. The rest of the address lines are set to one.
Figure 4-19 CPU Space Encoding for Interrupt Acknowledge
Because address match logic functions only after the EBI transfers an interrupt ac-
knowledge cycle to the external address bus following IARB contention, chip-select
logic generates AVEC
or DSACK signals only in response to interrupt requests from
external IRQ
pins. If an internal module makes an interrupt request of a certain priority,
and the chip-select base address and option registers are programmed to generate
AVEC
or DSACK signals in response to an interrupt acknowledge cycle for that priority
level, chip-select logic does not respond to the interrupt acknowledge cycle, and the
internal module supplies a vector number and generates an internal DSACK
signal to
terminate the cycle.
Perform the following operations before using a chip select to generate an interrupt ac-
knowledge signal.
1. Program the base address field to all ones.
2. Program block size to no more than 64 Kbytes, so that the address comparator
checks ADDR[19:16] against the corresponding bits in the base address regis-
ter. (The CPU32 places the CPU32 space type on ADDR[19:16].)
3. Set the R/W
field to read only. An interrupt acknowledge cycle is performed as
a read cycle.
4. Set the BYTE field to lower byte when using a 16-bit port, as the external vector
for a 16-bit port is fetched from the lower byte. Set the BYTE field to upper byte
when using an 8-bit port.
If an interrupting device does not provide a vector number, an autovector acknowledge
must be generated. Asserting AVEC
, either by asserting the AVEC pin or by generat-
ing AVEC
internally using the chip-select option register, terminates the bus cycle.
4.8.4 Chip-Select Reset Operation
The least significant bits of each of the 2-bit CS[10:0] pin assignment fields in CSPAR0
and CSPAR1 each have a reset value of one. The reset values of the most significant
bits of each field are determined by the states of DATA[7:1] during reset. There are
CPU SPACE IACK TIM
11111111111111111111 1111
LEVEL
19 1623
FUNCTION
CODE
20 0
CPU SPACE
TYPE FIELD
ADDRESS BUS
INTERRUPT
ACKNOWLEDGE
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Freescale Semiconductor, Inc.
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