Delay Time Programming 6-3
the data over the RS-485 bus. This data is normally command data being
sent to a module on the bus. When the RS-232 command data is complete,
the A2400 immediately turns its RS-485 transceiver back to receive mode
and monitors the RS-485 bus.
In normal operation the A2400 looks for a D series response prompt
character, either a ‘*’ or ‘?’. When a response prompt is received, the A2400
begins the first delay time , T1. Meanwhile, the A2400 stores the response
data from the module until a carriage return character is detected, signifying
the end of the response string. The A2400 checks to see if delay time T1 has
expired. If not, it waits until the delay is complete. After T1 is done, the A2400
activates the RTS signal to key the radio transmitter. After the RTS signal
is activated, delay time T2 is started to allow the transmitter to settle. After
the completion of delay time T2, the A2400 then checks for an active (high)
CTS line from the radio, then outputs the buffered response data to the RS-
232 Transmit line. When the transmit data is complete, the A2400 starts
delay time T3. After the completion of delay time T3, the A2400 turns off the
RTS signal and is now ready for the next command - response sequence.
Note that T1 only guarantees a minimum turn-around delay time. The actual
time is a function of the response time of the module and the amount of time
necessary for the radio’s transmitter to turn off after the RTS signal becomes
inactive.
If for some reason there is no response to a command, no RTS signal is
generated and the transmitter will not be keyed on. This allows the module
addressing to be spread among several radio modems on the same
frequency. For example, radio modem #1 could be connected to modules
with addresses of 1, 2, 3, and radio modem #2 could be connected to
modules with addresses of 4, 5, 6. The modems can operate on the same
frequency without interference since only the correctly addressed modules
will return response data.
The commands used to specify the delay times are similar to other D series
commands, using the standard format for analog data with the time values
scaled in milliseconds:
Command:
$1T1+00100.00
(set T1 to 100 ms.)
Response:
*
Command:
$1T2+00350.00
(set T2 to 350 ms.)
Response:
*
Summary of Contents for OMEGABUS A2400
Page 19: ...Communication 3 3...
Page 54: ...Extended Addressing 9 2 Figure 7 1 Typical system overview...
Page 64: ...Transparent Mode 10 5 Example 4 A2400 interfacing several instruments with a string of modules...
Page 65: ...Transparent Mode 10 6 Figure 10 5 Adding secondary control using A2400 modules...
