MC68331 Datasheet, PDF (34/84 Pages) Motorola, Inc – User’s Manual

Freescale Semiconductor, Inc.
SPACE —Address Space
Use this option field to select an address space for the chip-select logic. The CPU32 normally operates
in supervisor or user space, but interrupt acknowledge cycles must take place in CPU space.
Space Field
00
01
10
11
Address Space
CPU Space
User Space
Supervisor Space
Supervisor/User Space
IPL —Interrupt Priority Level
If the space field is set for CPU space (00), chip-select logic can be used for interrupt acknowledge.
During an interrupt acknowledge cycle, the priority level on address lines ADDR[3:1] is compared to the
value in the IPL field. If the values are the same, a chip select is asserted, provided that other option
register conditions are met. The following table shows IPL field encoding.
IPL
Description
000
Any Level
001
IPL1
010
IPL2
011
IPL3
100
IPL4
101
IPL5
110
IPL6
111
IPL7
This field only affects the response of chip selects and does not affect interrupt recognition by the CPU.
Any level means that chip select is asserted regardless of the level of the interrupt acknowledge cycle.
AVEC —Autovector Enable
0 = External interrupt vector enabled
1 = Autovector enabled
This field selects one of two methods of acquiring the interrupt vector during the interrupt acknowledge
cycle. It is not usually used in conjunction with a chip-select pin.
If the chip select is configured to trigger on an interrupt acknowledge cycle (SPACE = 00) and the AVEC
field is set to one, the chip select automatically generates an AVEC in response to the interrupt cycle.
Otherwise, the vector must be supplied by the requesting device.
The AVEC bit must not be used in synchronous mode, as autovector response timing can vary because
of ECLK synchronization.
3.5.5 Port C Data Register
Bit values in port C determine the state of chip-select pins used for discrete output. When a pin is as-
signed as a discrete output, the value in this register appears at the output. This is a read/write register.
Bit 7 is not used. Writing to this bit has no effect, and it always returns zero when read.
PORTC — Port C Data Register
15
RESET:
NOT USED
$YFFA41
8
7
6
5
4
3
2
1
0
0
PC6 PC5 PC4 PC3 PC2 PC1 PC0
0
1
1
1
1
1
1
1
34
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