Rockwell Automation 1771-DB BASIC MODULE - Manual (Page 298)

Chapter
Call Routines 69–127 13
13 -40
Modem Handshaking for Half-Duplex Mode
Modem handshaking Operational codes Description
half-duplex no
handshaking 0–3
•
RTS output line is activated during transmission, but no RTS On Delay or RTS Off
Delay is performed.
•
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
•
CTS and DSR input lines are not monitored nor do they have any affect on
transmissions or receptions.
•
Transmission monitor guarantees that transmitter interrupts are generated in a timely
manner. If a time-out occurs as a data packet was transmitting, the DF1_Status is set
to code value 5. Also, RTS is immediately dropped when this timeout occurs.
half-duplex without
continuous carrier 4–7 Important: For proper operation, connect the Data Carrier Detect (DCD) line from the
modem to the DSR input of port PRT2.
•
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.
•
Actual transmission does not start until the CTS input is active. A transmission
guarantees that transmitter interrupts are generated in a timely manner. If a timeout
occurs while a data packet is transmitting, then the DF1_Status is set to code value 5.
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; you may deactivate it via CALL
98, page 13 -34.
•
Characters 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.
half-duplex with
continuous carries 8–11 Important: For proper operation, connect the Data Carrier Detect (DCD) line from the
modem to the DSR input of port PRT2.
•
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.
•
Actual transmission does not start until the CTS input is active. A transmission
guarantees that transmitter interrupts are 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. Even after the DF1 Driver is disabled or remains
active, you may deactivate it via CALL 98, page 13 -34.
•
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.