EasyCoder 4420/4440 Bar Code Label Printer User’s Manual
4-8
Preventing Data Loss
Several problems can cause data loss or communications problems on the printer. Data
loss can result in printing errors or missing field data.
The printer is a serial ASCII device. It communicates with the host through an ASCII
serial communications I/O port. Hardware handshaking involves the use of a hardware
wire. Software handshaking involves a two-way datalink between the devices. The two
devices communicate with each other without losing data through the use of
handshaking. The printer sends both forms of handshaking simultaneously when the
printer’s input buffer is full. Any loss of data can cause printing errors or missing data.
Hardware handshaking uses pins 11 or 20 of the RS-232 interface to control data flow.
When the printer is using Intermec Standard protocol, it holds pins 11 and 20 high
when it is ready to receive data. The printer holds the pins low when it is in one of the
following conditions:
•
Buffer full
•
Ribbon fault
•
No label stock
•
Label at strip pin
The printer uses XON/XOFF protocol for software handshaking. When the input buffer
is full, the printer transmits an XOFF character. This character alerts the host to the fact
that the printer buffer is full and cannot receive any more data. When the printer is
ready to receive more data, it sends the XON character.
To check for communications problems
1. Check the cabling from the printer to the host system.
2. Check the communications interfacing of the devices connected to the printer.
3. Check the printer for proper electrical operation of the I/O port.
4. Ensure the host system is not overrunning the printer input buffers.
5. Ensure the data string being sent to the printer contains the correct information.
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