Byte ModeThe printer and host send data to each other along eight data lines (one bit perline).If bidirectional communication is supported by the printer and the host, the hostwill take control of the data transfer.The Negotiation PhaseThe negotiation phase determines which operating mode will be used. At this time,the host and the printer will sense what devices are attached, the supported signalsavailable, and which mode to use. The selected mode, in turn, defines the pins onthe 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, depending on the modeselected. See Table 8 for the different connector signals.SignalsTable 8 lists each of the signals associated with the corresponding pins on the 1284interface. Descriptions of the signals follow.Table 8. 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 Xflag14 Host nAutoFd Host Busy HostAck15 Not Defined16 Logic Grid17 Chassis Grid18 Printer Peripheral Logic High19 Signal Ground (nStrobe)20 Signal Ground (Data 1)21 Signal Ground (Data 2)22 Signal Ground (Data 3)Chapter 5. Printer Interfaces 215
