B&B Electronics 232MSS2 Datasheet

232MSS2-0812ds -1/3

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Model 232MSS2

RS-232 Four-Port Mini

Smart Switch/Port Combiner

Description

The RS-232 Four Port Mini Smart Switch/Port Combiner, Model 232MSS2, allows one RS-232 host device to connect
to as many as four RS-232 devices. The 232MSS2 can function as a software and/or hardware controlled switch. As a
software controlled switch, referred to as smart switch mode, the device connected to the master port of the 232MSS2
has control over which one of the four ports it is connected to. As a hardware controlled switch, referred to as port
combiner mode, the handshake lines of the devices connected to the four ports are used to gain access to the master
port. More details of smart switch and port combiner modes are covered later in this datasheet.

There are four LED's on the 232MSS2 to indicate which port is connected to the master port. The master port has a
DB-25S female connector and the slave ports have DB-9S female connectors. The master port can be configured as a
DTE or DCE port by an internal switch setting (See Table 1). If the master port is configured as a DTE port, the four
slave ports will become DCE ports. The 232MSS2 supports the following signals: TD, RD, RTS, and CTS. Handshake
lines DSR and DTR are connected together and are not passed through to the master port. There is no delay through
the device and data is not buffered. The 232MSS2 will work with baud rates from 1200 to 115,200 bps; 7 or 8 data bits;
even, odd or no parity; and 1 or 2 stop bits (7,N, 1 is not allowed). The communication format is set via dipswitch 1
(SW1 -- See Table 1).

NOTE: The data format and rates mentioned are used to switch the 232MSS2. Communication between the devices
can use any format or data rate.

Operation

Smart Switch Mode
The switch can be controlled in two different ways. The first way is referred to as smart switch mode. In this mode, the
switch is controlled by sending a programmable three-character preamble code to the "Master" port of the 232MSS2.
The first character of the preamble code must be the ASCII “Escape” character (decimal 27). The second character is
user programmable by setting Dipswitch 2 (SW2 -- See Table 2). The third character should be the ASCII upper case
letters A, B, C, or D to select the appropriate port. The third character can also be the ASCII “EOT” (decimal 4)

character, which will turn off all the ports. Example: To select port “A”, send the ASCII “ESC” character, the

programmable character and the “A” character. When the 232MSS2 receives this code the master port will be
connected directly to port “A”.

Port Combiner Mode

The other way to control the switch is referred to as port combiner mode. In port combiner mode, a slave port can gain
access to the master port by asserting a handshake line (CTS for DTE slave ports, RTS for DCE slave ports). If a slave
port asserts its handshake line and no other slave ports have their handshake line asserted, the master port will then be
connected directly to the slave port with the asserted handshake line. Once a slave port is connected to the master
port, the connection will remain until the slave disasserts its handshake line. If multiple slave ports have their
handshake lines asserted, access will be granted on a first come-first serve basis. If none of the slave ports have their
handshake line asserted, the switch can be controlled using the preamble codes.

Example: (Initial conditions--no slave ports with handshake lines asserted) In chronological order, Port C asserts its
handshake line, Port A asserts its handshake line, Port D asserts its handshake line and then Port C disasserts its
handshake line. When Port C asserts its handshake line, a connection will be made between the master port and Port
C. When Port C disasserts its handshake line, Port C will disconnected and Port A will be connected to the master port.
When Port A disasserts its handshake, Port A will be disconnected and Port D will be connected to the master port.

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International Office: 707 Dayton Road PO Box 1040 Ottawa, IL 61350 USA 815-433-5100 Fax [phone]

European Office: Westlink Commercial Park Oranmore Co. Galway Ireland [phone] Fax [phone]

PRODUCT INFORMATION B&B ELECTRONICS

Timer Features

Table 1 - Communication & Port Setup

Dipswitch SW1

Setting

1 2 3 4 5 6 7

8

0 0 0 X X X X X 1200 Baud

1 0 0 X X X X X 2400 Baud

0 1 0 X X X X X 4800 Baud

1 1 0 X X X X X 9600 Baud*

0 0 1 X X X X X 19.2K Baud

1 0 1 X X X X X 38.4K Baud

0 1 1 X X X X X 57.6K Baud

1 1 1 X X X X X 115.2K Baud

X X X 0 X X X X Enhanced Disabled *

X X X 1 X X X X Enhanced Enable

X X X X 0 X X X 8 Data Bits *

X X X X 1 X X X 7 Data Bits

X X X X X 0 X X Parity Disabled *

X X X X X 1 X X Parity Enabled

X X X X X X 0 X Smart Switch Mode*

X X X X X X 1 X Port Combiner Mode

X X X X X X X 0 DCE master port *

X X X X X X X 1 DTE master port

0 = OFF 1 = ON X = DON'T CARE

*Factory defaults

Table 2

Programmable Character Setting

Dipswitch SW2*

Weight

1 1 2 2 3 4 4 8 5

16 6 32 7 64 8 128

*Factory Default --ASCII “STX” character

(decimal 2), SW2 position is only one ON.

Table 3 - Timer Values

Data Byte

Value

0

timer disabled

1

10ms

2

25ms

3

100ms

4

500ms

5

1 s 6 5 s

7

30 s

8

1 min.

9

5 min.

The 232MSS2 has an enhanced mode, which offers special
timer features. The timer features can be used to prevent slave
devices from receiving preamble commands, inadvertent
switching from binary/graphic file transfers, and inactive slave
devices from holding control of the master port. The timer has
two different modes: an inactivity mode and an inadvertent
switch mode. When in inactivity mode, the 232MSS2 will
monitor the data lines. If there is no activity for the specified
time, the selected slave port will be disconnected from the
master port. When in inadvertent switch mode, the 232MSS2
will ignore switching commands for the specified time. After
this time has expired, the selected slave port will be
disconnected from the master port.

Timer functions are enabled via a dipswitch setting and
through software commands. Software commands follow the
same format as preamble codes used for switching. Two
commands are used to set the timer functions: Set Timer Mode
and Set Timer Value. These commands require an additional
byte for data. The Set Timer Value command requires the third

byte to be an ASCII “T” character. The data byte (fourth byte)
must be a value between ASCII “0” and ASCII “9”. A value of
“0” is used to disable the timer. Refer to Table 3 for timer

values.

The Set Timer Mode command requires the third byte to be an ASCII “M”. If the
data byte (fourth byte) is an ASCII “0” (default), the timer will be setup as an

inactivity timer. When the timer is configured as an inactivity timer, the 232MSS2
will monitor the data lines (TD & RD) for data. If there is no activity for the
specified timer value, the slave port that is connected to the master port will be
disconnected. In smart switch mode, the inactivity timer can be used to prevent
the preamble codes from being received by the slave devices. In port combiner
mode, the inactivity timer can be used to prevent devices from tying up the master
port. For example (port combiner mode): All the slave ports have their handshake
lines asserted. The device on Port C has its handshake line asserted and is
currently connected to the master port, but has not been transmitting or receiving
data. When the inactivity timer expires, Port C will be disconnected and the next
slave port will then be connected to the master port (following the first come-first

serve rule). Port C will then be placed at the “end of the line”.

If the data byte of the Set Timer Mode command is an ASCII “1”, the timer will be

set up to ignore switching commands. When the timer is configured in this mode,

the 232MSS2 will not accept any switching commands (“A”, ”B”, ”C”, ”D”, or

“EOT”) for the specified timer value. After the timer has expired the slave port that

is connected to the master port will be disconnected. This feature is useful to
prevent inadvertent switching during binary/graphic type file transfers. For
example (smart switch mode): the timer is configured to ignore switching
commands for 5 seconds. The select Port D command is sent to the 232MSS2.
Once Port D is connected a file of unknown data type (so file may or may not
contain a switching command sequence) is to be transferred through the
232MSS2. For a period of 5 seconds after Port D is connected, no switching
commands will be accepted. As long as the file transfer takes less than 5
seconds, there is no chance the 232MSS2 will inadvertently switch ports.

232MSS2-0812ds -2/3

© 2003 by B&B Electronics. All rights reserved.