HP Advanced Communications Controllers (ACC) manual Terminal State

ZCOM Message Handling

Terminal State

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.

	Terminal State	SEND	RECV
	Enabled/Activated	Yes	Yes
	Enabled/Deactivated	Yes	No
	Disabled/Activated	No	No
	Disabled/Deactivated	No	No
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).

34 Chapter 2