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(12) If the host selected the Reverse Idle phase and new data becomes available to be sent from
the printer, the printer sets PtrClk to Low to request the host for an interrupt. (Event 18)
(13) The printer sets PtrClk back to High. (Event 19)
(14) Upon receiving a request for interrupt from the printer, the host responds by setting HostBusy
(nAutoFd) to High. (Event 20)
(15) Finally, the printer responds to the host by setting AckDataReq (PError) to Low, and then the
host moves to the Host Busy Data Available phase. (Event 21)