Nibble Mode; Byte Mode; Signals - Printronix H-SERIES P7000 User Manual

Chapter 5
IEEE 1284 Parallel Interface

Nibble Mode

Eight bits equals one byte. When a byte of data is sent to the printer, the eight
bits are sent over eight data lines.
Some devices cannot send data over their eight data lines. To bypass this,
the 1284 permits data to be sent as half a byte over four status lines. (Half a
byte equals one nibble.) Two sequential four-bit nibbles are sent over the
lines.
Data is transferred from printer to host in four-bit nibbles over the status lines,
and the host controls the transmission.

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.

Signals

Table 7 lists each of the signals associated with the corresponding pins on the
1284 interface. Descriptions of the signals follow.
Pin
1 Host
2 Host/Printer
3 Host/Printer
4 Host/Printer
5 Host/Printer
6 Host/Printer
7 Host/Printer
8 Host/Printer
9 Host/Printer
10 Printer
11 Printer
12 Printer
13 Printer
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Table 7. 1284 Signals
Source of Data
Compatible
nStrobe
Data 1 (LSB)
Data 2
Data 3
Data 4
Data 5
Data 6
Data 7
Data 8 (MSB)
nAck
Busy
PError
Select
Type of Mode
Nibble Byte
HostClk Host/Clk
PtrClk PtrClk
PtrBusy PtrBusy
AckDataReq AckDataReq
Xflag Xflag