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Port B (I/O address 61h) supports the following settings. Bits 0 to 3 are read/write,
bits 4 to 7 are read-only
KEYB
PRNMI
D7
Bit
Name
7
PRNMI
6
IONMI
5
SP
4
RF
3
IOCHK
2
PR
1
SPON
0
SPCOU
INOMI
SP
r
r
r
D6
D5
Function
parity error occurred
0
=
no NMI from parity error
1
=
parity active, NMI requested
I/O error occurrend
0
=
no NMI from IOCHK
1
=
IOCHK active, NMI requested
Loudspesker counter signal
Refresh detection,changing with the refresh cycle (15 s)
I/O channel check
0
=
enabled
1
=
disabled and erased
Parity checking on systom board
0
=
enabled
1
=
disabled and erased
Direct speaker control
0
=
speaker off
1
=
speaker on
Loudspeaker counter gate
0
=
counter disabled
1
=
counter disabled
SF
IOCHK
PR
r
r/w
r/w
D4
D3
D2
SPON
SPCOU
r/w
r/w
D1
D0
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