User's Manual

CHAPTER 3
Performing Advanced Functions
42
Notifications
Notifications are frames sent asynchronously by devices that are
otherwise slaves. The notifications are received by a device closest
to the host and then sent to the host. If the host is not available,
the receiving device will store the notification and wait until it is
questioned by the host. At this point, it will inform the host that it
has a notification. It is then the task of the host to issue a command
to read the respective notification.
Before a device can issue a notification, the notification must first
be enabled. Special frames are used to this end, depending on the
notification type. If an end device is not able to send a notification
due to radio propagation or other kind of communication prob-
lems, it will store the date/time when the notification took place.
As soon as the communication is re-established, the device will try
to send the notification again.
Note: To avoid collisions, the device will wait a random time (up to
10 seconds) before sending the notification frame.
When the device closest to the host receives a notification from a
remote, it must inform the host about it by sending a break charac-
ter on the serial line. The host must then issue the command DEV
in order to see which device has a notification pending. If the host
is not available, the device closest to the host will wait until first
time requested by the host and after answering to the host request
will re-send a break. This sequence will go on as described until the
host issues the DEV command.
The following notification is currently defined for the A723 Series 4
device:
• NOPC—Notification On Port Change (see “PORT” on
page 34).
Returned errors list
Following are error messages you might get.
Command line interpreter
• 1 — nonexistent command
• 2 — command line buffer overflow (input line too long)
• 3 — internal error