IBM 6500-V1P Maintenance Manual - Page 174
Device Handshaking, The Printer Interface, Communication Problems, Hardware Handshaking
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Communication Problems Table 4. Common Communications Problems Problem Interface Common Causes Cannot access the printer through PMU over an Ethernet Interface (continued from previous page) Host cannot communicate with 6500 printer when hooked up to TCP/IP to AS/400 with the Ethernet NIC installed ethernet ethernet 12. Press STOP to exit the menu and put the printer in the NOT READY state. 13. Power off the printer, wait a few seconds, then power on the printer to activate the new diagnostic port. The PMU will now establish a connection with the Ethernet Interface. Refer to the appropriate Ethernet Interface User's Manual. Device Handshaking Handshaking is the exchange of signals between the host computer and the printer to indicate the status of the data being transferred. In serial data transfer, the printer uses both hardware and software handshaking and transmits both forms simultaneously when the input buffer is full. The printer can be used with either serial or parallel host interfaces. Parallel interfaces are usually straightforward, with no special settings required. Serial interfaces, however, have a variety of possible communication parameter settings. There are two methods of handshaking: • Hardware Handshaking This is an electrical signal controlled by the logic state on pin 20 of the serial interface connector J2 at the back of the printer. The signal goes high when the printer is ready to receive data. The signal goes low when the printer is in the busy state, which indicates that the input buffer is full and can no longer receive data. • Software Handshaking XON and XOFF are software signals that control serial data flow between the printer and the host system. When the printer input buffer is full, the printer transmits the XOFF (CTRL S) character, which signals the host to stop sending data. When space becomes available in the input buffer, the printer sends the XON (CTRL Q) character, which tells the host that the printer is ready to receive more data. The Printer Interface The printer will not function properly if an incorrectly wired interface cable or the wrong interface cable is installed. 174