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PK-232 TECHNICAL MANUAL
Bit
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PB7
PB6
PB5
PB4
PB3
PB2
PB1
PB0
PC2
PC1
PC0
The Busy and ACK signals should each contain a 200-Ohm series resistor in the cable to
the parallel printer.
3.3.4
8530 SCC Serial Communications Controller
U7 is an 8530 SCC chip which provides two serial communications ports.
Port A is the HDLC port for Packet-Radio.
Port B is the RS-232 interface to the terminal.
This chip receives address bits A0, A1 and A7 from the CPU. The PK-232 firmware ad-
dresses the 8530 by forcing all other address bits high, yielding these addresses:
$7C - Terminal (Port B) control
$7D - Terminal (Port B) data
$7E - HDLC (Port A) control
$7F - HDLC (Port A) data
The 8530 chip has a 2.4576 MHz clock that is totally independent of the rest of the sys-
tem.
The serial interface signals TXD (J2 pin 2), RTS (4) and DTR (20) flow from the RS-232
connector through the drivers on the 1489 chip at U19 to the 8530's RXDB, CTSB and
DCDB pins respectively.
The 8530 output pins TXDB, RTSB and DTRB pins are buffered by the drivers on the 1488
chip at U20 to the J2 pins RXD (3), CTS (5) and DCD (8) respectively.
Both the RTS (J2 pin 4) and DTR (pin 20) signals must be high for the 8530 to send data
on the RS-232 link.
J2 pin 8 (DCD) may be used as an active-high Packet Connect indicator for mailbox soft-
ware. J2 pin 6 (DSR) is permanently pulled high. J2 pin 1 is frame ground and J2 pin 7 is
signal ground. All other J2 pins are reserved for use with a parallel printer.
The SYNCB input (pin 29) is pulled high by R179. This input may be connected to a hard-
ware EAS (Echo as Sent) switch to monitor the output in AMTOR, Morse, Baudot and AS-
CII modes.
Forcing this pin low has the same effect as typing the command
PK232TM Rev. A 5/87
U6 Pin
J2 Pin
15
21
14
19
13
18
12
17
11
16
10
15
9
14
8
13
21
24
20
23
19
22
Function
Sense
Data 8
Pos
Data 7
Pos
Data 6
Pos
Data 5
Pos
Data 4
Pos
Data 3
Pos
Data 2
Pos
Data 1
Pos
Busy
Pos
Ack
Neg
Strobe
Neg
3-6
CHAPTER 3 – THEORY OF OPERATION
Direction
Out
Out
Out
Out
Out
Out
Out
Out
In
In
Out
EAS
ON.
Page 16
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Table of Contents
Troubleshooting
