Reference Guide

ZCOM Message Handling
Terminal State
Chapter 234
Terminal State
Within the ZCOM subsystem, the terminal state may be either enabled
or disabled, activated or deactivated. For normal I/O operations, a
terminal ZLU must be both enabled and activated. If a terminal is
disabled (regardless of whether it is activated), then no messages can be
sent to it or received from it.
If a terminal is enabled but deactivated, then messages can be sent to
the terminal, but none can be received. The following table illustrates
the different combinations.
NOTE A terminal state of disabled overrides the activated/deactivated status.
For some protocols (such as the NCR 301 protocol), the protocol handler
automatically deactivates the terminal when a valid message is received
and until it has been processed. Each time a message is received, the
terminal must be reactivated by the receiving program, using the zcntl
command with the ‘activate’ request code (request code 9,
ZCOM_MRQCODE_ACT).
Terminal State SEND RECV
Enabled/Activated Yes Yes
Enabled/Deactivated Yes No
Disabled/Activated No No
Disabled/Deactivated No No