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).