HP LaserJet 4 Service Manual - Page 428

Infrared Communication The HP LaserJet 5, 5M, and 5N 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 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 B-5. The LAP and LMP layers can reside in either firmware, software, or a combination of both. There are different LAP and LMP protocols for primary and secondary devices. The HP LaserJet 5 printer has the complete secondary protocol, and any host trying to communicate via the infrared (IR) port must have the complete primary protocol installed. The primary protocol software is the responsibility of the host supplier. It is not provided by Hewlett-Packard with the printer. IrDA host (or primary device) communications can be obtained either via an internal IR port or an external IR accessory. Several manufacturers offer complete accessory upgrades for both host and peripheral devices. B-34 LaserJet 5/5M/5N Printer