Atari 400 Technical Reference Manual page 493

PIA ADDRESSES
WRITE READ
Address Name Description Name Description
D3FF
I
Repeat as shown below many times
D304
D303 PBCTL PORT B CONTROL PBCTL Same as write
D302
PACTL PORT A CONTROL PACTL Same as write
Direction Register
PORTB If PBCTL Bit 2-0 PORTB Same as write
D301
(otherwise)
Jack 2
&
Jack 3 Jack 2 &
Jack
PORTB If Direction Bits PORTB If Direction
Are 1
*
Are 0
*
Direction Register
PORTA
If PACTL Bit 2=0 PORTA Same as write
D300 (Otherwise)
Jack 0
&
Jack 1
Jack
o
&
Jack
PORTA If Direction Bits PORTA If Direction
Are 1
*
Are 0
*
*
NOTE: Output data is retained in Jack Output Registers.
If direction bits are true, a read of the jacks
will read old data from these registers.
3
Bits
1
Bits