FSR IT-VCM - Manual (Page 15)

Page 15 of 16
Passing Serial Requests
Multiple RS-232 controlled devices can be present on the same serial port. This type of setup is a
multi-drop configuration. The IT-VCM will be capable of passing strings down a drop through the
use of a drop preamble that determines the position on the drop of the device for which the serial
data is intended.
Passing serial requests down to a device will only work if FSR products that support passing
requests are between the RN8200, RN1000, WPCS or other control system and the last device on the
drop. Only the last device on the drop can be a non-multidrop FSR product or other manufacturer’s
product.
The message is made up of two parts, the drop preamble and the string data. The message is
terminated with a carriage return (0x0D).
Drop Preamble
The drop preamble contains a skip indicator (‘\S’) for each device that will pass the string along.
The preamble will be enclosed in braces ({}). For example, if the user wished to send a string to the
third device on a drop, the preamble would be "{\S\S}".
For example; {\S\S}"Another test Message <0D>" <CR>.
The first device would, upon detecting the preamble start, strip off the \S and send the preamble
down as "{\S}". The second device, detecting the preamble start would strip off the other \S. It
would also sense the close brace "}" and would be responsible for removing it from the string. The
second device would also be responsible for converting any ASCII-Hex characters into pure hex,
and for sending the complete message to the third device.
String Data
The string data would be enclosed in double quotes; this allows a string of data to be virtually any
length. Single Hex characters will be defined as <0D> (which is a carriage return). Multiple hex
characters can be sent using the same scheme but with spaces between the two ASCII bytes that
represent the hex value (example <0A 0D> which is a carriage return and line feed). A backslash
character will be used preceding a "<" or ">" if the "<" or ">" is part of the string but not defining
ASCII-Hex characters. An example of this might be "\< is a less than character" or "\> is a greater
than character". If a backslash is part of a string a double backslash will be sent "\\". If a double
quote is required in a string it would be sent as "\"".
In order to pass a request to a device connected to the IT-VCM, a pass through sequence must be
sent from a RN8200, RN1000, WPCS or other control system. Using "\S" for each device on the
drop enclosed in braces ({}). For example, in the case of an FSR IT-R4S; {\S\S}"R 1 1<CR>"
would cause the first device on the drop to skip the request and send "[\S]R 1 1<CR>" to the second
device on the drop. (continued on next page)