TallyGenicom LMPPLS Administrator's Manual

Contents

TallyGenicom LMPPLS Administrator's Manual Manual pdf 95 page image

95Centronics Parallel Interface SignalsData Lines 1 through 8. Provides eight standard or inverted levels from the host that specify characterdata, plot data, or a control code. Data Line 8 allows access to the extended ASCII character set. Youmay enable or disable this line via the Data Bit 8 parameter on the Centronics submenu.Data Strobe. Carries a low true, 100 ns minimum pulse from the host that clocks data into the printer.Acknowledge. A low true pulse from the printer indicating the character or function code has beenreceived and the printer is ready for the next data transfer.Online. A high true level from the printer to indicate the printer is ready for data transfer and the ONLINEkey on the control panel has been activated. When the printer is in online mode, it may accept data fromthe host.Paper Empty (PE). A high true level from the printer to indicate the printer is in a paper empty or paperjam fault.Busy. A high true level from the printer to indicate the printer cannot receive data.Prime. A high true level from the host to indicate the printer should perform a warm start (printer is resetto the power-up configuration values).Paper Instruction (PI). Carries a CVFU signal from the host with the same timing and polarity as the dataline.Fault. A low true level from the printer indicates a printer fault.IEEE 1284 Parallel InterfaceThe 1284 supports three operating modes, which are determined by negotiation between the printer andthe host.Compatibility ModeThis mode provides compatibility with Centronics-like host I/O (see Table 9). Data is transferred from thehost to the printer in 8-bit bytes over the data lines.Compatibility Mode can be combined with Nibble and Byte Modes to provide bidirectional communication.Nibble ModeEight bits equals one byte. When a byte of data is sent to the printer, the eight bits are sent over eightdata lines.Some devices cannot send data over their eight data lines. To bypass this, the 1284 permits data to besent as half a byte over four status lines. (Half a byte equals one nibble.) Two sequential four-bit nibblesare sent over the lines.Data is transferred from printer to host in four-bit nibbles over the status lines, and the host controls thetransmission.Byte ModeThe printer and host send data to each other along eight data lines (one bit per line).If bidirectional communication is supported by the printer and the host, the host will take control of thedata transfer.SignalsTable 9 lists each of the signals associated with the corresponding pins on the 1284 interface.Descriptions of the signals follow.