User`s guide

AD1 ... AD8 (Data 1 ... Data 8)
Negotiation Phase: Extendibility request value.
Reverse Data Transfer
Phase:
Nibble Mode: NOT USED.
Byte Mode: Reverse channel data.
PrtClk (nAck)
Compatibility Mode: Pulsed low by the printer to acknowledge the transfer of a data from the host.
Negotiation Phase: Set low to acknowledge 1284 support, then set high to indicate that the Xflag (Select)
and data available flags may be read.
Reverse Data Transfer
Phase:
Used in both Nibble and Byte Modes to qualify data being sent to the host.
PrtBusy (Busy)
Compatibility Mode: Driven high to indicate that the printer is not ready to receive data.
Negotiation Phase: Reflects the present state of the printer's forward channel.
Reverse Data Transfer
Phase:
Nibble Mode: Data bits 3 then 7, then forward channel busy status
Byte Mode: Forward channel busy status.
Reverse Idle phase: Forward channel busy status.
AckDataReq (PError)
Compatibility Mode: Driven high to indicate that the printer has encountered an error in the paper path. The
printer shall set nFault low whenever it sets PError high.
Negotiation Phase: Set high to indicate 1284 support, then follows nDataAvail (nFault).
Reverse Data Transfer
Phase:
Nibble Mode: Data bits then 6.
Byte Mode: same as nDataAvail (nFault)
Reverse Idle phase: Set high until host requests data transfer, then follows nDataAvail (nFault).
Xflag (Select)
Compatibility Mode: Set high to indicate that the printer in on-line.
Negotiation Phase: The Xflag refers to extendibility flag. Used by the printer to reply to the requested
extendibility byte sent by the host during the negotiation phase. The signal level is low for
Nibble Mode, high for Byte Mode.
Reverse Data Transfer
Phase:
Nibble Mode: Data bits 1 then 5.
Byte Mode: Same as negotiation phase.
Reverse Idle phase: Same as negotiation phase.
Xflag (Select)
Compatibility Mode: Set low by host to put the printer into auto-line feed mode.
Negotiation Phase: Set low in conjunction with 1284 Active (NSelectIn) being set high to request a 1284
mode.
Then set high after printer sets PtrClk (nAck) low.
332 Programmer Manual