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He's talking about the ODB connector (The data link connector (DLC)).
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ISO 9141-2 K-line.

Let me explain this one thing that most people don't know about the 1994 - 2002 Chrysler odb.

Now PIN 7 (SCI TRANSMIT) isn't just SCI it's actually special ISO 9141-2 K-line circuit combined with the SCI Tx line.
ISO-K-line allows two-way communication on a single line for generic scan tool.
Data is transferred at a fixed baud rate of 10.4K bps.
Scan tool biases the circuit to 12 volts.
The data is transferred when the 12-volt bias is pulled low.

K-line Initialization.
ISO 9141-2 K-line knows a 5 baud initialization sequence. The Scan tool must start this init by transmitting byte 0x33 to the verhicle at 5 bits per second.
The total transmit time for transmitting byte 0x33 takes about 2 seconds.
After this initialization it is expected to continue communicating at 10k4 baud.

CHRYSLER DRB III Diagnostic Scanner use this most of the time.
SCI - Serial Communication Interface.
SCI consists of:
– Dedicated point-to-point, dual-wire, nonmultiplexed serial communication interface
– Supports both diagnostics and flash reprogramming capability
– Supports multiple baud rates to accommodate
both the low-speed diagnostic command mode (at 7812.5 bps) and the high-speed parameter
interrogation command mode (at 62,500K bps).
The scan tool supplies the bias 5v to the module on the Tx circuit
The module pulls the voltage low to transmit data to the scan tool
The module supplies bias 5v on the Rx circuit.
The scan tool pulls the voltage low to send data to the module
Therefore, the component receiving the data supplies the bias 5v.

TX and RX are abbreviations for Transmit and Receive, respectively.
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