Epson TM-U950P - B/W Dot-matrix Printer Specification page 156

12) Whenever the printer generates data for the host in the Reverse Idle phase, it sets PtrClk
low to request an interrupt from the host (event 18).
13) Then, the printer sets PtrClk high (event 19).
14) The host responds to the interrupt requested by the printer by setting HostBusy(nAutoFd)
high (event 20).
15) The printer then sets AckDataReq(PError) low to acknowledge the host s response,
followed by the transition of the interface to the Host Busy Data Available phase (event 21).
J.2.5.2 Byte Mode
1) After negotiating to the Byte Mode, the host will place the data line in a high impedance
state (event 14) then set HostBusy(nAutoFd) low (event 7) to indicate that it is ready to
accept data from the printer.
2) The printer responds by placing the communication data on the data line (event 15).
3) The printer then sets PtrClk(nAck) low (event 9).
4) The host latches data in the event 9 then sets HostBusy(nAutoFd) high, indicating that it is
processing the data(event 10).
5) At this point, the printer shall respond by setting the status line as follows (event 13).
• PtrBusy(Busy):
• nDataAvail(nFault):
• AckDataReq(PError):
• Xflag(Select):
6) The printer then sets PtrClk(nAck) high, completing the byte handshake (event 11).
7) At this point, the host will pulse HostClk(nStrobe) low (event 16), then high (event 17),
signaling that it has received the byte.
8) Note that the events 10 and 16 may occur simultaneously, and the events 7 and 17 may
occur simultaneously (in such cases in which HostBusy and HostClk are set equivalent).
9) At the end of a byte transfer, the printer reports to the host whether or not it has additional
data to transmit to the host. When the printer has no more data, the host is allowed three
options as listed below.
1. To proceed with termination and return to Compatibility Mode.
2. To remain in the Host Busy Data Not Available phase.
3. To set HostBusy(nAutoFd) low then put the interface into the Reverse Idle phase (event
7).
To its current forward channel value
Low if another byte is ready to be sent
To the same value as nDataAvail(nFault)
To its value during the last negotiation or low