IBM 3151 User Manual page 141

Reference Information (SYSTEM ATTACH)
Write Host Message Command
Differences
Function
Format
The command syntax is changed.
Writes a host message into the OIA.
If the message is longer than 80 or 132 characters (80- or 132-column mode,
respectively), the overflow characters are written at the cursor position (when in
cursor address mode) or the buffer address (when in buffer address mode).
ESC
#
= message ESC
=
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User's Guide for the Cartridge to Emulate IBM and DEC Terminals