D12
EX-IR
Gas Transmitter with IR Smart Sensor
Dec 2019 ( 85-0004 Rev A)
63
A delay of up to 10 seconds can be added after each line is transmitted to help prevent buffer overflows
on printers without XON/XOFF protocol. This is sometimes required to allow slow printers enough time
to perform carriage return. If characters appear to be missing, increase the setting.
Flow Control
The transmitter uses XON/XOFF flow control while sending a report. That is, once the data stream has
begun, it will continue until the XOFF character (19) is received. After sitting idle, the report stream will
begin again upon reception of the XON character (17).
An RS232 connection can support full duplex communication and is perfectly suited for XON/XOFF
flow control. However, an RS485 connection is only half duplex. It cannot receive while it is
transmitting and might miss the XOFF character, resulting in a buffer overflow at the receiving device.
A receiving device will send the XOFF character when its buffer is nearly full. Some older dot-matrix
printers will send an XOFF because they have a small receive buffers and cannot process characters while
the head is returning to start a new line. By comparison, most computers have comparatively large
buffers and can easily accept the report stream without sending an XOFF, so an RS485 connection may
work in those cases.
The transmitter features an additional method to help avoid losing data due to buffer overflow problems
on receiving devices that lack XON/XOFF capability (or have the capability but are using an RS485
connection). A programmable time delay of up to 10s may be inserted at the end of each report line.
This permits the receiver time to process more characters in its buffer and avoid an overflow. However,
this may be a method of trial and error until the proper delay setting is determined so that no characters
are missing from the report.
