C-1
Appendix C. Limitations of the Talk-
Through Mode
When using talk-through mode, other aspects of the SDM-SIO4 can be affected or limited.
This Appendix lists these limitations.
C.1 Limitations
The talk-through mode is entered by issuing a command of the form T x:y,
where x is the SDM-SIO4 address and y is the port number (0 for the command
line mode). See the datalogger manual for further details.
When talking through to any of the four serial ports, the baud rate, word length,
parity and handshake mode are as set previously by the PORTSET command or
by the datalogger program.
Once in this mode, any characters typed, or sent from the PC, are transmitted
via the SDM-SIO4 to the relevant port. The datalogger polls the SDM-SIO4 at
a frequency of approximately 10Hz to pick up any characters received on the
relevant port and transmits them back to the PC. This mode of operation is
slower than a direct serial connection, but is fast enough for most purposes.
If you talk-through to a serial port, that port will not be available for use by the
datalogger program currently running. No characters will be sent out, nor
received, from that port under program control. This will usually result in out of
range values being stored if data is being read from that port by the program.
The talk-through mode is terminated by a 40 second time-out. The timeout is
reset by characters being sent from the PC to the SDM-SIO4 via the datalogger.
If no characters are received after 40 seconds the talk through mode will be
cancelled and all ports returned to normal operation.
When using talk-through in command line mode the following limitations
apply:
1.
if the datalogger is running a program that includes P113 instructions that
require a lot of processing of data or reconfiguration of the SDM-SIO4,
then the speed of response and data transfer to and from the serial port in
question will slow down. In some cases, characters sent from the PC may
not be received by the SDM-SIO4, as it gives the highest priority to other
tasks. Therefore you either need to check the commands sent are received
correctly, or even stop the datalogger program if this appears to be a
problem with your talk-through sessions.
2.
the commands RAMTEST and RESET will cause talk-through mode to
exit. This is because these commands ‘take over’ the SDM-SIO4 for a
time, which makes it unresponsive to communication attempts by the
datalogger. The commands still function, but to get the result from the
RAMTEST command you will have to wait long enough for the command
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