MORE INFORMATION
XON/XOFF is software handshaking. Handshaking is accomplished by the
exchange of control codes between the printer and the server via the
transmit and receive lines, pins 2 and 3 respectively (RS232-C). When the
printer's data buffer is full, it sends an XOFF telling the server's print
processor to pause output. When the buffer has available space for more
data, an XON character is sent and the server continues to send until the
next XOFF. For example, when you type a long text document to your screen,
the data scrolls off the screen too rapidly for you to read. When you press
CTRL+S, you are sending an XOFF control character. XOFF tells the processor
to pause the screen output until you've finished reading. Output continues
when the processor receives a CTRL+Q (XON). The printer talks to the server
in the same manner. This XON/XOFF handshaking continues until the server
has sent the entire spool file.
XON/XOFF handshaking is adequate for most serial communication needs and
can easily be set up on the server by selecting the correct parameters on
the mode and 3mode lines. A sample XON/XOFF mode statement is shown further
below in example 1.
Hardware handshaking uses signal voltage levels instead of control code to
communicate between DTE and DCE devices. There are several signal options
that can be used. The most common signals used are Data Terminal Ready
(DTR) pin 20 on the printer, which is connected to Clear To Send (CTS) pin
5 and Data Set Ready (DSR) pin 6 on the server. When the printer data
buffer fills, the voltage level on pin 20, DTR, changes from high to low.
This tells the server to stop sending data. When the buffer has available
space for more data, the DTR voltage level toggles high and the server
continues to send until the next DTR voltage drop.
Hardware handshaking is the default setting (see example 2 below). The
minimum parameters needed for hardware handshaking are shown in example 3.
Note that DTR can be set to either ON or HS with the same outcome.
Sample COM Port Configurations (excerpt from C:\LANMAN\NETPROG\SETMODE.CMD)
Example 1: XON/XOFF
c:\os2\mode
COM1:9600,N,8,1,TO=OFF,XON=ON,IDSR=OFF,ODSR=OFF,OCTS=OFF,DTR=OFF,RTS=OFF
>> startup.log 2>>&1
c:\os2\mode COM1: >> startup.log 2>>&1
c:\3mode COM1;9600;n;8;1;0; >> c:\startup.log 2>>&1
Example 2: Hardware (default settings)
c:\os2\mode
COM1:9600,N,8,1,TO=OFF,XON=OFF,IDSR=ON,ODSR=ON,OCTS=ON,DTR=ON,RTS=ON
>> startup.log 2>>&1
c:\os2\mode COM1: >> startup.log 2>>&1
c:\3mode COM1;9600;n;8;1;1; >> c:\startup.log 2>>&1
Example 3: Hardware (minimal settings)
c:\os2\mode
COM1:9600,N,8,1,TO=OFF,XON=OFF,IDSR=OFF,ODSR=ON,OCTS=OFF,DTR=ON(hs),
RTS=OFF >> startup.log 2>>&1
c:\os2\mode COM1: >> startup.log 2>>&1
c:\3mode COM1:9600;n;8;1;1; >> c:\startup.log 2>>&1
Testing was done with the following equipment and settings:
3Com 3S500 server with LAN Manager 2.1, both COM 1 and COM 3 tested
E-Z Interface IBM XT - HP printer cable
HP 7550a plotter:
Data flow = Remote standalone
Handshake = Hardware
Bypass = Off
Duplex = Full
Parity = 8 Bit, off
Baud rate = 9600