Rockwell Automation 1746-BAS BASIC LANGUAGE - Manual (Page 144)

Publication 1746-RM001A-US-P
11-14 Status Functions
Half-Duplex No Handshaking Modem Control
Half-duplex no handshaking modem control, selected by operational codes 0
through 3, has the following characteristics:
•
The RTS output line is activated during transmission, but no RTS On Delay
or RTS Off Delay is performed.
•
The DTR output line is not manipulated by the DF1 driver. It is
recommended that you activate DTR in your BASIC program while DF1
communications are taking place
•
The CTS and DSR input lines are not monitored nor do they have any affect
on transmissions or receptions.
•
A transmission monitor guarantees that transmitter interrupts are being
generated in a timely manner. If a timeout occurs, the DF1_Status is set to
code value 5 if a data packet was being transmitted. Also, RTS is immediately
dropped when this timeout occurs.
Half-duplex without continuous carrier modem control, selected by operational
codes 4 through 7, 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.
Even after the DF1 Driver is disabled, it will remain active; the user may
deactivate it via a BASIC Call.
•
Characters that are received only are accepted if the DCD line is active. A
packet reception is aborted if DCD goes inactive during the byte-to-byte
reception of that packet.
There is no constant monitoring of DCD even between packets as there is with
the constant carrier selection. Therefore, the DTR line is never deactivated.
IMPORTANT
For proper operation, the Data Carrier Detect (DCD) line from
the modem must be connected to the DSR input of port PRT2.