HP 5M manual Serial Pin-out and Cabling Configuration, Serial Communication

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Serial Pin-out and Cabling Configuration

	Serial Communication
	Serial communication is simply the transmission of data one bit at a time.
	With just one bit to transmit at a time, data can be transferred with a simple
	electrical circuit consisting of only two wires. In this fashion an eight bit
	byte is transmitted one bit at a time and the individual bits are reassembled
	into the original byte on the receiving end. Bit transmission occurs from
	the least significant bit to the most significant bit.
Data Terminal	Transmit on pin 2 and receive on pin 3. A printer is typically a DTE device.
Equipment (DTE)
Data	Transmit on pin 3 and receive on pin 2. A modem is typically a DCE device.
Communications
Equipment (DCE)
Asynchronous	Asynchronous communication or start/stop transmission is the concept of enclosing a character
Communication	with a start and stop bit. The RS-232 specification defines the standards for asynchronous serial
	communication.
Parity	Parity is a method of error checking in which a bit is added to keep the number of bits in a
	character even or odd depending upon whether or not even or odd parity is used.
HP LaserJet Serial	Transmission is asynchronous, with one start bit, eight data bits and one stop bit. Parity is not
Data Format	used. HP LaserJets are DTE devices.
Serial Interface	Handshaking is the method in which the flow of data between two devices is controlled. The two
Protocol	methods of flow control that are used by HP LaserJet printers are software flow control, in which
(handshaking)	one device controls another by the content of the data and hardware flow control, in which one
	device can control another by changing the voltage on a wire.
Software Flow	Xon/Xoff is a data stream handshake protocol which sends Xon (DC1; 11 Hex) to the computer
Control (software	from the printer’s transmit data pin when the printer is able to accept data and sends Xoff (DC3; 13
handshaking)	Hex) when the printer is not ready for data.
Hardware Flow	By definition hardware handshaking is performed when two programs manipulate RS-232 control
Control (hardware	pins-DTR, DSR, RTS, and CTS to achieve a hardware-based form of flow control. In DTR/DSR
handshaking)	handshaking, the sender asserts DTR (Data Terminal Ready) before sending the first character in
	a stream of data and waits for DSR (Data Set Ready) to be asserted in return. RTS/CTS
	handshaking is similar, but uses the Request To Send and Clear To Send pins rather than Data
	Terminal Ready. In either case, the sender delays transmitting data until the receiver is ready.

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