R/W — Read/Write
This field causes a chip select to be asserted only for a read, only for a write, or for
both read and write.
STRB — Address Strobe/Data Strobe
0 = Address strobe
1 = Data strobe
DSACK — Data Strobe Acknowledge
This field specifies the source of DSACK in asynchronous bus mode and controls wait
state insertion.
SPACE — Address Space Select
This field selects an address space to be used by the chip-select logic.
IPL — Interrupt Priority Level
This field determines interrupt priority level when a chip select is used for interrupt ac-
knowledge. It does not affect CPU interrupt recognition.
AVEC — Autovector Enable
Do not enable autovector support when in synchronous mode.
0 = External interrupt vector enabled
1 = Autovector enabled
D
Table D-12 Option Register Function Summary
MODE
BYTE
R/W
STRB
DSACK
SPACE
IPL
AVEC
0 = ASYNC 00 = Disable 00 = Rsvd 0 = AS 0000 = 0 WAIT 00 = CPU SP
000 = All
0 = Off
1 = SYNC
01 = Lower
10 = Upper
11 = Both
01 = Read 1 = DS 0001 = 1 WAIT 01 = User SP 001 = Priority 1 1 = On
10 = Write
11 = Both
0010 = 2 WAIT 10 = Supv SP 010 = Priority 2
0011 = 3 WAIT 11 = S/U SP 011 = Priority 3
0100 = 4 WAIT
0101 = 5 WAIT
0110 = 6 WAIT
0111 = 7 WAIT
1000 = 8 WAIT
1001 = 9 WAIT
1010 = 10 WAIT
1011 = 11 WAIT
1100 = 12 WAIT
1101 = 13 WAIT
1110 = F term
100 = Priority 4
101 = Priority 5
110 = Priority 6
111 = Priority 7
1111 = External
MOTOROLA
D-24
REGISTER SUMMARY
MC68331
USER’S MANUAL
MOTOROLA [ MOTOROLA ]
