Intel 386 - Manual (Page 223)

Intel386™ EX EMBEDDED MICROPROCESSOR USER’S MANUAL
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9.3.6 Initialization Command Word 4 (ICW4)
Use ICW4 to select the special-fully nested mode or the fully nested mode and to enable the au-
tomatic EOI mode.
Figure 9-12. Initialization Command Word 4 Register (ICW4)
Initialization Command Word 4
ICW4 (master and slave)
(write only)
Expanded Addr:
ISA Addr:
Reset State:
master slave
F021H F0A1H
0021H 00A1H
XXH XXH
7 0
0 0 0 SFNM 0 0 AEOI
1
Bit
Number
Bit
Mnemonic
Function
7–5 — Write zero to these bits to guarantee device operation.
4 SFNM Special-fully Nested Mode:
0 = Selects fully nested mode.
1 = Selects special-fully nested mode. Only the master 82C59A can
operate in special-fully nested mode.
3–2 — Write zero to these bits to guarantee device operation.
1 AEOI Automatic EOI Mode:
0 = Disables automatic EOI mode.
1 = Enables automatic EOI mode. Only the master 82C59A can operate
in automatic EOI mode.
0 — Write one to this bit to guarantee device operation.