RFL SMX3 / 21
Page 11 of 22
Issue 1.4
User Manual
08 June 2009
9. V.24 Data Ports (Channels B & C)
Ports B and C are DCE ports on DB9 female connectors for asynchronous data:
Channels B & C Ports Pin-out – D9F on chassis (DCE)
Circuit Pin
Direction
TxD Transmit
Data
3
Input
RxD Receive
Data
2
Output
RTS
Request to Send
7
Input
CTS
Clear to Send
8
Output
DCD
Data Carrier Detect
1
Output
DTR
Data Terminal Ready
4
Input
DSR
Data Set Ready
6
Output
RI Ring
Indicator
9
Output
SG Signal
Ground
5
Screen / Drain must be connected to the connector Shell
RI is permanently OFF.
DSR is ON when aggregate framing is synchronised.
DTR is ignored.
RTS turns on remote DCD and local CTS after a delay.
Transceivers are specified to ± 15kV IEC1000-4-2 air discharge ESD protection and
port connections are additionally protected by Tranzorb type arrays.
DIP switches provide configure options for each port, see section 10.
V.24 Port Sharing
There are two methods by which multiple V.24 ports can be assigned to an
aggregate channel:
Channels (ports) B and C within an SMX3/21 unit are assignable to
Aggregate Channels 2 and / or 3.
Where two SMX3s are co-located and interconnected via the concatenation
ports, it is possible for each of Channels B & C to be selected to communicate
over either via X.21 aggregate channel or the concatenation port in which
cases the channel terminates within the SMX3/21, via both ports, for daisy-
chain applications via a co-located SMX3/21.
Where multiple V.24 ports are assigned to a channel (on one or multiple
SMX3/21 units), data from the channel is presented at RxD of all ports other
than the source of the data, and data to the channel is an ‘or’ function of TxD
of those ports where RTS is asserted ON. It is important therefore that
equipment connected in this way, such as a SCADA system, has the self-
discipline for only one to be transmitting at any time.
