HP C3916A HP LaserJet 5, 5M, and 5N Printer - User's Guide - Page 189

Serial Communication

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E 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 Equipment (DTE) Transmit on pin 2 and receive on pin 3. A printer is typically a DTE device. Data Communications Equipment (DCE) Transmit on pin 3 and receive on pin 2. A modem is typically a DCE device. Asynchronous Communication Asynchronous communication or start/stop transmission is the concept of enclosing a character 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 Protocol (handshaking) Handshaking is the method in which the flow of data between two devices is controlled. The two methods of flow control that are used by HP LaserJet printers are software flow control, in which 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 Control (software handshaking) Xon/Xoff is a data stream handshake protocol which sends Xon (DC1; 11 Hex) to the computer from the printer's transmit data pin when the printer is able to accept data and sends Xoff (DC3; 13 Hex) when the printer is not ready for data. Hardware Flow Control (hardware handshaking) By definition hardware handshaking is performed when two programs manipulate RS-232 control pins-DTR, DSR, RTS, and CTS to achieve a hardware-based form of flow control. In DTR/DSR 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. EN Serial Pin-out and Cabling Configuration E-1

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E
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
Equipment (DTE)
Transmit on pin 2 and receive on pin 3. A printer is typically a DTE device.
Data
Communications
Equipment (DCE)
Transmit on pin 3 and receive on pin 2.
A modem is typically a DCE device.
Asynchronous
Communication
Asynchronous communication or start/stop transmission is the concept of enclosing a character
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
Data Format
Transmission is asynchronous, with one start bit, eight data bits and one stop bit.
Parity is not
used. HP LaserJets are DTE devices.
Serial Interface
Protocol
(handshaking)
Handshaking is the method in which the flow of data between two devices is controlled.
The two
methods of flow control that are used by HP LaserJet printers are software flow control, in which
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
Control (software
handshaking)
Xon/Xoff is a data stream handshake protocol which sends Xon (DC1; 11 Hex) to the computer
from the printer’s transmit data pin when the printer is able to accept data and sends Xoff (DC3; 13
Hex) when the printer is not ready for data.
Hardware Flow
Control (hardware
handshaking)
By definition hardware handshaking is performed when two programs manipulate RS-232 control
pins-DTR, DSR, RTS, and CTS to achieve a hardware-based form of flow control.
In DTR/DSR
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.
EN
Serial Pin-out and Cabling Configuration
E-1