Rockwell Automation 1746-BAS BASIC LANGUAGE - Manual (Page 145)

Publication 1746-RM001A-US-P
Status Functions 11-15
Half-Duplex With Continuous Carrier Modem Control
Half-duplex with continuous carrier modem control, selected by operational codes
8 through 11, has the following characteristics:
•
The RTS output line is activated only during transmissions. The actual packet
transmission starts after the delay specified by the RTS On Delay parameter,
assuming the CTS input is active by then. When the transmission is complete
and the delay time period specified by the RTS Off Delay parameter has timed
out, RTS is deactivated.
•
An actual transmission does not start until the CTS input is active. A
transmission guarantees that transmitter interrupts are being generated in a
timely manner. If a timeout occurs, then the DF1_Status is set to code value 5
if the data packet was being transmitted. RTS is dropped immediately when
this occurs.
•
If not already active, the DTR line is raised when the DF1 Driver is enabled. It
is dropped only when DCD is lost as described in the next paragraph. Even
after the DF1 Driver is disabled or remains active, the user may deactivate it via
a BASIC CALL.
•
For packet reception, the DCD signal is monitored (via the DSR input line).
If DCD is not already active when the DF1 Driver is enabled, then it is
immediately detected when it does go active. At this point, the DCD is
checked every 5 ms to make sure it remains active. If DCD goes inactive, the
driver waits 10 seconds for it to go active again. If DCD does not go active
again in this amount of time, then the DTR output line is dropped for a period
of time ranging from 5 to 10 ms in length.
Also, characters that are received are accepted if the DCD line is active. A
packet reception is aborted if DCD goes inactive during the byte-to-byte
reception of a packet.
IMPORTANT
For proper operation, the Data Carrier Detect (DCD) line from
the modem must be connected to the DSR input of port PRT2.