Despatch 926E Equipment Manual (C-155)Rev 2/11 - Manual (Page 53)

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XON/XOFF Protocol
Your Watlow control is selectable for use with one of two protocols:

XON/XOFF, used when one master controls one Watlow.

ANSI X3.28-1976 Sub 2.2 and A3, used to address multiple units in a single
serial (RS-422/485) line.
The XON/XOFF protocol on the Watlow uses a as a message terminator. The
ANSI X3.28... uses various control characters (e.g., ETX, EOT).
The black box converter is a "smart" converter, which automatically takes care of much
of the IEEE488 parallel side protocol. However, it requires either a carriage return or
line feed text terminator on the serial side (RS-232, 422) in order for the converter to
know when to time certain functions. For this reason, the Watlow control must be
configured for XON/XOFF protocol.
This also means that each Watlow device is going to need its own converter, and each
converter will need a unique IEEE address.
XON/XOFF Versus RTS/CTS Handshaking
Watlow interface ports do not support RTS/CTS handshaking so the black box
converter must be configured for XON/XOFF also. (See dip switch settings.) Also,
there must be a jumper between RTS and CTS pins in the black box DB25 serial
connector. If you use Despatch-supplied cabling, the jumper is supplied within the
cabling.