Citizen CLP-621, Technical Manual

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2-4. Interface
2-51
CLP-621 & CLP-631
2-4-2. Parallel Interface
( 1) Specifications
Transmission system 8-bit parallel data
Receive buffer size
16K bytes
Transmission modes Compatible mode
It is an asynchronous forward channel mode to send the byte width
data from the host to the printer. The interface line of the data is
operated in accordance with signal line definitions of Centronics.
NIBBLE mode
It is an asynchronous reverse channel mode to send the data from
the printer to the host. In Nibble mode, 4-bit data (half byte) is sent at
a time using the 4 status lines (FAULT, SELECT, PE, and BUSY). To
send one complete byte data, the printer sends 2 nibbles (8 bits in
total) to the host. Nibble mode is usually combined with Compatible
mode to create a complete bi-directional channel.
ECP mode
ECP mode permits bi-directional asynchronous data transmission,
and by means of interlock handshake, it does not require the timing
necessary with Compatible mode.
Signal level IEEE1284 compatible
( 2) Signal line and pin assignment
Pin No. Signal name I/O Function in Compatible Mode
1 STROBE Input Strobe signal to read in 8-bit data
2-9 DATA0-7 Input 8-bit parallel signal
10 ACKNLG Output 8-bit data request signal
11 BUSY Output Signal specifying printer busy
12 PERROR Output Signal specifying media end
13 SELECT Output Signal specifying if the printer is on-line (printing enabled)
or off-line
14 AUTOFD Input Invalid (ignored)
15 NC --- Not used
16 SGND --- Signal ground
17 FGND --- Frame ground
18 P.L.H Output Peripheral logic high (pulled up to +5V at 1K Ω )
19-30 GND --- Ground for twisted pair return
31 PRIME Input Printer reset
32 FAULT Output Signal specifying printer error
33 GND --- Signal ground
34 NC --- Not used
35 FUSE --- Not used
36 SELECTIN Input Invalid (ignored)