Rockwell Automation 1771-DB BASIC MODULE - Manual (Page 300)

Chapter
Call Routines 69–127 13
13 -42
Modem Handshaking for Full-Duplex Mode
Modem handshaking Operational codes Description
full-duplex with no
handshaking 16–23
•
RTS output line is activated when the DF1 Driver is enabled and remains so until the DF1
Driver is disabled.
•
DTR output line is not manipulated by the DF1 Driver. It is recommended that you
activate DTR (CALL 97, page 13 -33) in your BASIC program while the DF1
communications is taking place.
•
CTS and DSR input lines are not monitored or have any effect on transmissions.
•
Transmission monitor 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 not deactivated when this timeout occurs.
full-duplex modem
(FDM) 24–31
•
RTS output line is activated when the DF1 Driver is enabled and remains so until the DF1
Driver is disabled.
•
An actual transmission does not start until the CTS input is active. A transmission
monitor guarantees that transmitter interrupts are generated in a timely manner. If a
timeout occurs when a data packet is transmitting, then the DF1_Status is set to code
value 5. RTS is not deactivated when this occurs.
•
If DTR is not already active when the DF1 Driver is enabled, it is immediately activated.
It becomes active only if DCD is lost as described in the next paragraph. Even after the
DF1 Driver is disabled, DTR remains active; you may deactivate it via CALL 98, page
13 -34.
•
For packet receptions, 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, DCD is checked every 5 ms to make sure it remains active.
If it goes inactive, the driver waits 10 seconds for DCD to go active again. If DCD does
not go active again in this amount of time, then the DTR output line is deactivated for a
period of time ranging from 5 to 10 ms in length.
Also, characters that are received are only 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.
Input Argument Two
The second input argument specifies the poll time-out period when in
half-duplex mode or the ACKnowledge time-out period when in
full-duplex mode. Poll time-out specifies in 5 ms increments how long to
wait before being polled by the DF1 master, before a transmission request
is ignored. PUSHing 0 indicates no poll time-out period. ACKnowledge
time-out specifies in 5 ms increments how long to wait for an ACK/NAK
before transmitting an ENQuiry. The valid range for the ACKnowledge
time-out is 2 to 65535.