HP LaserJet 5p/mp Service Manual - Page 122

HP LaserJet 5P/5MP, 6P/6MP Printer Service Supplement New Product Features Infrared Communication The HP LaserJet 5P/5MP and 6P/6MP printers are equipped with an Infrared Datalink Association (IrDA) compliant port. The IrDA specification allows "wireless" transmission of print data between a wide variety of hosts (primary) and peripheral (secondary) devices. A primary device -- such as a PC or laptop computer -- is capable of reading and writing data to another primary device or writing to a secondary device, such as a printer. Secondary devices are read-only; they cannot initiate their own communication, and can only respond to a host command when properly addressed. The IR port works by receiving data similarly to a serial port, but without a cable. The port's speed depends on the printer model: • HP Laserjet 5P/5MP printer • 115 k bits per second • HP Laserjet 6P/6MP printer • up to 4 megabits per second When the IR connection is established, the status light comes on. If the connection is broken or when the print job is complete, the status light goes off. The IrDA protocol uses a transceiver chip in both devices to send and receive data packets. The packets are checked for validity, and a response is sent by the secondary device indicating whether the packets were complete or in error. The IrDA protocol is contained in three layers: • The physical electronics are the hardware elements in each device for sending and receiving the data. • The Link Access Protocol (LAP) layer controls the physical layer, packetizes/unpacketizes data, and sets transmission rates. • The Link Management Protocol (LMP) layer routes data to and from the host operating system (DOS/Windows). The data flow is shown in Figure 8. 19