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Table 7.6. Parallel user
port
information (continued).
Pin
Signal
Signal
Identification
Character
label
Description
6
Tape #1
Used with the diagnostic routine to
READ
verify cassette tape #1 read function,
7
Tape
#2
Used with the diagnostic routine to
READ
verify cassette tape #2 read function.
8
Tape Write
Used with the diagnostic routine to
verify operation of the WR ITE func·
tion of both cassette ports.
9
TV.
T.
V. vertical sync signal verified in
Vertical
diagnostic. May be used for external
TV display.
10
1. V.
T. V. horizontal signal verified in
Horizontal
diagnostic may be used for TV display.
11, 12
GND
Digital ground.
A
GND
Digital ground.
S
CA1
Standard edge sensitive input of
6522VIA.
C
PA0
0
PA1
Input/output lines to peripherals,
E
PA2
f--
and can be programmed in depend·
F
PA3
ently of each other for input
or output.
H
PA4
J
PA5
K
PA6
L
PA7
M
CS2
SpeciallfO pin of VIA.
N
GND
Digital ground.
VERSATILE INTERFACE ADAPTER
The lines on the bottom side of the user port connector originate from a Versatile Interface Adapter
(VIA MOS Technology part #6522).
The signals CA1, PAO·7, and CB2, are directly connected to a standard 6522 VIA located at hexadecimal
address E840. (Decimal address 59456).
The parallel port consists of eight programmable bi-directional I/O lines PAO·7, an input handshake line
for the eight lines,CA1, which can also be used for other edge-sensative inputs and a very powerful
connection, CB2. This has most of the abilities of CA1, but can also act as the input or output of the VIA
shift register.
A detailed specification for the VIA is below. All signals on the VIA that are not connected to the user
port are utilized by the PET for internal controls. Please note that the user should avoid interfacing these
signals in any way.
60
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