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b) Port B (I/O address = 06lH)
Data setting to the register is performed by writing to
the I/O address 06lH.
Getting the data from the register is performed by
reading the same address.
The meaning of each bit of the
register is as follows.
When mode register bit4
=
"1"
Bit
Description
I
PA 0
+ TImer 2 Gate speaker
1
+ Speaker data
N
2
Not used
P
3
Read high Ilow switch
4
- Enable RAM parity check
U
5
- Enable I/O channel check
6
- Hold keyboard elK low
T
7
- (Enabled keyboard)
Each bit of the register (PC bit) after power on reset is
as followsJ
BIT
State
c) Port C (I/O address
=
062H)
Data setting to the register is performed by writing to
the I/O address 062H.
Acquiring the data from the register is performed by
reading the same address when bit 0 (PCO-3) and bit 3
(PC4-7) of the mode control register are set to "0".
Bit 0 and 3 of the mode register are usually set to "1"
(when power on reset) and the following data is acquired
when read operation is executed.
When mode register bit4
=
"1"
Bit
PB7
=
"0"
PB7
=
"0"
I
PA 0
...
N
1
2
P
3
keyboard
4
,.. Input
U
5
data
6
T
7
A - 13
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