Epson EPL-5700 Reference Manual page 94

Nibble mode: Not used
ECP mode: Bi-directional data
nACK/PtrClk/PeriphClk
All modes: DTA8 is the MSB, DATA1 is the LSB
Compatibility mode: Acknowledgment low pulse in order to
indicate that data was transferred from the host
Negotiation phase: Low signal indicates IEEE 1284 is supported;
Set to high afterwards to indicate that the Xflag and "data
available" flag are valid
Reverse data transfer phase: In nibble mode, a low signal indicates
that the nibble data is valid
Reverse idle phase: When switched from low to high, generates
an interrupt that notifies the host that there is data available.
ECP mode: Used to transfer data from the printer to the host with
handshaking via HostAck (nAutoFd)
Busy/PtrBusy/PeriphClk
Compatibility mode: High signal indicates that the printer is not
ready to receive data
Negotiation phase: Reflects the BUSY status of the forward
channel
Reverse data transfer phase: In nibble mode, this signal serves as
nibble data bit 3 and then 7
Reverse idle phase: Reflects the BUSY status of the forward
channel
ECP mode: Used for forward direction flow control. In reverse
direction, this signal is used as a ninth data bit that indicates
whether the data signals indicate a command or data.
A-8
Technical Specifications