ICS ELECTRONICS 9099, Инструкция по эксплуатации

Страница: 75 / 178

3-29
3
LAN systems have multiple timeouts. There is the VXI-11 IO_timeout which
includes the wait-for-lock-release time and the delays in the module. In the
case of the 9099 this also includes the modbus serial timeout value set by the
D command. The VISA communication or RPC network timeouts are long
timeouts designed to catch network failures.
COMM_Timeout is unique to ICS VXI-11 devices and refers to the time the
device's service will go without getting a message from the other party before
declaring the link dead. KeepAlive is a background function of the device’s
TCP/IP Stack to check the socket connection and is invisible to the applica-
tion. Both of these functions will terminate a broken link or channel, release
any locks and release the resources for use by another link. Else the device
can run out of resources and become inaccessible. There is also a lock timeout
that sets the time a command will wait for a device lock to be released before
timing out.
COMM_Timeout should be set to a low period like 2 minutes (factory setting)
when you are first debugging a program and tend to breakout of the program
without properly closing the sockets. Power cycle a unit to clear up any open
sockets. Later, with a finished program, extend the COMM_Timeout to several
hours to avoid prematurely closing the socket while you are not communicating
with the 9099. Hard wired systems are pretty dependable and you can safely
extend the 9099’s COMM_Timeout to a day. Do not set COMM_Timeout to
0, which disables the timeout, unless you have a way to physically reset the
9099 if it runs out of resources.
The 9099’s Keep_Alive function should be enabled. Keep_Alive will put a
short message on the network, once every 2 hours if there has been no traffic
from the client in this time.
The recommendation is to install a background function in your test program
to prevent unwanted socket closure during work breaks or unplanned test stop-
pages. This function can be set to perform some RPC VXI-11 activity through
the socket when nothing has been done for a period of time less than the 9099's
COMM_Timeout setting. The background functions should not alter the state
of the devices or of the interface. Some non-altering actions are opening and
closing a second link to the 9099. All channels need to be exercised once in
each instruments' COMM_Timeout period.