260Chapter 5 IEEE 1284 Parallel InterfaceByte ModeThe printer and host send data to each other along eight data lines (one bitper line).If bidirectional communication is supported by the printer and the host, thehost will take control of the data transfer.The Negotiation PhaseThe negotiation phase determines which operating mode will be used. At thistime, the host and the printer will sense what devices are attached, thesupported signals available, and which mode to use. The selected mode, inturn, defines the pins on the 1284 connector.There are 36 pins on the parallel interface. Each one sends a different signal.Pin 1, for example, can send a Strobe signal or a HostC1k signal, dependingon the mode selected. See Table 10 for the different connector signals.SignalsTable 10 lists each of the signals associated with the corresponding pins onthe 1284 interface. Descriptions of the signals follow.Table 10. 1284 SignalsPin Source of DataType of ModeCompatible Nibble Byte1 Host nStrobe HostClk Host/Clk2 Host/Printer Data 1 (LSB)3 Host/Printer Data 24 Host/Printer Data 35 Host/Printer Data 46 Host/Printer Data 57 Host/Printer Data 68 Host/Printer Data 79 Host/Printer Data 8 (MSB)10 Printer nAck PtrClk PtrClk11 Printer Busy PtrBusy PtrBusy12 Printer PError AckDataReq AckDataReq13 Printer Select Xflag Xflag
