Documentation Number 232PTC0812 - pg. 1/2
www.bb-elec.com orders@bb-elec.com support@bb-elec.com
International Office: 707 Dayton Road PO Box 1040 Ottawa, IL 61350 USA 815-433-5100 Fax 433-
5104
European Office: Westlink Commercial Park Oranmore Co Galway Ireland +353 91 792444 Fax +353 91 792445
PRODUCT INFORMATION B&B ELECTRONICS
RS-232 Port Combiner
Model 232PTC
Introduction
B&B Electronics’ Model 232PTC permits two or more serial devices to share
a serial port on a host computer. When one of the devices on either of the slave ports transmits data, it captures
the data path to the master port and locks out the other slave port. When data transmission is finished, either
slave port gets access to the master port by being the first to start sending data. The RTS line can also be used to
control data flow to the master port. The 232PTC can be cascaded to combine as many devices as needed into
one host port. A typical application would be to share one host port with several terminals, scanners, scales, or
other devices that only need access to the host port occasionally as shown in Figure 1.
Operation
Data flow from master port to slave ports
All data that is sent to the TX line, pin 2 on the master port, is broadcast to
both slave ports under all conditions. This data appears on pin 3 of each
slave port.
Data flow from slave ports to master port
Data that is sent to the TX line (pin 2) on the slave ports must compete for
the path to the master port. There are two methods of capturing the path
to the master port, RTS and automatic data sensing. The first slave port to
either raise its RTS line or transmit data captures the path to the master
port. The path will be locked on that slave port until it either lowers its RTS
line, or 50 milliseconds after the end of its transmission. Note that the
232PTC does not buffer any data, any data sent to the opposite slave port
during this period will be lost. The 50ms timeout period can be modified,
contact B&B’s technical support for further information.
Handshake Signals
The CTS signal on each slave port indicates to the slave devices if
the path to the master port is available. If the slave port’s CTS line is
high, data received by that port will be transmitted out the master port.
If CTS is low, the opposite slave port has captured the path to the
master and any data at the inactive slave port will be lost. For
example, if both slave ports are inactive and have RTS low, CTS will
be high at both slave ports, indicating that the path is available. As
soon as one slave port captures the path by either beginning its
transmission or raising its RTS line, the CTS signal at the opposite
slave port will drop to the low state.
The RTS output on the pin 4 of the master port follows the RTS signal
level found on the active slave port.
Pinouts
All ports on the 232PTC are configured as RS-232 DCE ports, using DB25 female connectors. Note that a null-
modem type connection will be required to connect the 232PTC to other DCE configured ports. Tables 1 and 2
and Figure 1 show the configuration of each port.
Figure 1: Application Example
