Dynapro Technologies Dynapro ET TCS, Руководство разработчика приложений

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To make interfacing as trouble-free as possible, the TCS features easily configured
communication parameters. This configurability takes some care to manage. Usually a report in
the Operational Status Window of the Setup Screen provides a tip if there are any problems, but
sometimes the communication link is not properly established, and yet no message appears.
Assume the host is configured to communicate using 7 data bits and ignoring parity. Even though
parity is ignored, the bit is still present, so the host sends and expects to receive 8 bits (7 data bits
+ l parity bit). Setting the TCS to use 8 data bits and no parity does not cause a Framing Error
message, because the framing formats actually do match
−
they are both set for 8 bits. Neither end
uses parity, so a Parity Error is not reported either. This kind of mistake can be avoided by
having all applications set the host parameters and TCS parameters to exactly match.
Other possible communication problems that generate no messages include:
•
Setting multidrop addresses but never using multidrop protocol or hardware
•
Not setting multidrop addresses, then trying to use multidrop protocol or hardware
•
Using a minimum 3-wire RS-232-E cable and attempting to implement control line
handshaking
•
Connecting to the host using a null modem cable when a straight-through cable is required or
vice-versa
•
Setting XON/XOFF mode to OFF, then attempting to use software handshaking. (This
eventually could result in a Buffer Overflow error.)
•
Setting the TCS for LOCAL operation, then attempting to communicate with it from a
remote host
•
Setting a multidrop address but not saving it. If the host program now sends a Soft Reset
command, the address reverts the “none” (default).