The Negotiation Phase; Signals - IBM 6400 Setup Manual

Byte Mode
The 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 the data transfer.

The Negotiation Phase

The negotiation phase determines which operating mode will be used. At this
time, the host and the printer will sense what devices are attached, the
supported signals available, and which mode to use. The selected mode, in
turn, defines the pins on the 1284 connector.
There are 36 pins on the parallel interface. Each one sends a different signal.
Pin 1, for example, can send a Strobe signal or a HostClk signal, depending
on the mode selected. Table 5–5 on page 5–15 shows the different
definitions.

Signals

1284 interface signals between the host and the printer are defined below.
Host Clock / nWrite – Driven by host. Data transferred from host to printer.
When printer sends data, two types are available. If Nibble Mode, signal is
set high. If Byte Mode, signal is set low.
Data 1 through Data 8 – These pins are host–driven in Compatibility Mode
and bidirectional in Byte Mode. They are not used in Nibble Mode. Data 1 is
the least significant bit; Data 8 is the most significant bit.
Printer Clock / Peripheral Clock / Interrupt – Driven by the printer. A signal
from the printer indicating the character or function code has been received
and the printer is ready for the next data transfer.
Printer Busy / Peripheral Acknowledge / nWait – Driven by the printer.
Indicates the printer cannot receive data. (Data bits 4 and 8 in Nibble Mode.)
Acknowledge Data Request / nAcknowledge Reverse – Driven by the printer.
Indicates the printer is in a fault condition. (Data bits 3 and 7 in Nibble
Mode.)
Xflag – Driven by the printer. A high true level indicating the printer is ready
for data transfer and the printer is on–line. (Data bits 2 and 6 in Nibble
Mode.)
5–14 6400 Line Matrix Printers Setup Guide, Cabinet and Pedestal Models