MC68F375
SINGLE-CHIP INTEGRATION MODULE 2 (SCIM2E)
MOTOROLA
REFERENCE MANUAL
Rev. 25 June 03
4-73
4.8.4 Interrupt Processing Summary
A summary of the entire interrupt processing sequence follows. When the sequence
begins, a valid interrupt service request has been detected and is pending.
1. The CPU32 finishes higher priority exception processing or reaches an instruc-
tion boundary.
2. Processor state is stacked.
3. The interrupt acknowledge cycle begins:
a. FC[2:0] are driven to 0b111 (CPU space) encoding.
b. The address bus is driven as follows. ADDR[23:20] = 0b1111
ADDR[19:16] = 0b1111, which indicates that the cycle is an interrupt
acknowledge
CPU
space
cycle;
ADDR[15:4]
=
0b111111111111;
ADDR[3:1] = the priority of the interrupt request being acknowledged; and
ADDR0 = 0b1.
c. Request priority is latched into the CCR IP field from the address bus.
4. Modules or external peripherals that have requested interrupt service decode
the priority value in ADDR[3:1]. Each module or device with a request level
equal to the value in ADDR[3:1] enters interrupt arbitration.
5. After arbitration, the interrupt acknowledge cycle is completed in one of the fol-
lowing ways:
a. When there is no contention (responding modules have IARB = 0b0000),
the internal bus monitor, if enabled, asserts BERR, and the CPU32
generates the spurious interrupt vector number.
b. The interrupt source that wins arbitration supplies a vector number and
DSACK signals appropriate to the access. The CPU32 acquires the
vector number.
c. The AVEC signal is asserted either by the external device requesting
interrupt service (AVEC can be tied low if all external interrupts are to use
autovectors) or by an appropriately programmed SCIM2E chip select, and
the CPU32 generates an autovector number corresponding to the
interrupt priority.
d. The bus monitor or external device asserts BERR and the CPU32
generates the spurious interrupt vector number.
6. The vector number is converted to a vector address.
7. The content of the vector address is loaded into the PC and the processor
transfers control to the exception handler routine.
4.9 Chip Selects
Typical microcontrollers require additional hardware to provide chip-select signals for
external devices. The SCIM2E includes nine programmable chip-select circuits that
can provide from 2- to 16-clock cycle access to external memory and peripherals.
Address block sizes of two Kbytes to one Mbyte can be selected. Figure 4-21 is a dia-
gram of a basic system that uses chip selects.
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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