M68HC16 Z SERIES
REGISTER SUMMARY
USER’S MANUAL
D-21
SPACE[1:0] — Address Space Select
Use this option field to select an address space for chip-select assertion or to configure
a chip-select as an interrupt acknowledge strobe for an external device. The CPU16
normally operates in supervisor mode only, but interrupt acknowledge cycles take
place in CPU space.
shows address space bit encodings.
IPL[2:0] — Interrupt Priority Level
When SPACE[1:0] is set for CPU space (%00), chip-select logic can be used as an
interrupt acknowledge strobe for an external device. During an interrupt acknowledge
cycle, the interrupt priority level is driven on address lines ADDR[3:1] and is then com-
pared to the value in IPL[2:0]. If the values match, an interrupt acknowledge strobe will
be generated on the particular chip-select pin, provided other option register condi-
tions are met.
shows IPL[2:0] field encoding.
AVEC — Autovector Enable
This field selects one of two methods of acquiring an interrupt vector during an inter-
rupt acknowledge cycle. This field is not applicable when SPACE[1:0] = %00.
0 = External interrupt vector enabled
1 = Autovector enabled
If the chip select is configured to trigger on an interrupt acknowledge cycle
(SPACE[1:0] = %00) and the AVEC field is set to one, the chip-select automatically
generates AVEC and completes the interrupt acknowledge cycle. Otherwise, the vec-
tor must be supplied by the requesting external device to complete the IACK read
cycle.
Table D-17 Address Space Bit Encodings
SPACE[1:0]
Address Space
00
CPU Space
01
User Space
10
Supervisor Space
11
Supervisor/User Space
Table D-18 Interrupt Priority Level Field Encoding
IPL[2:0]
Interrupt Priority Level
000
Any Level
1
NOTES:
1. Any level means that chip-select is assert-
ed regardless of the level of the interrupt
acknowledge cycle.
001
1
010
2
011
3
100
4
101
5
110
6
111
7
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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