Campbell Hausfeld Serial I/O Interface SDM-SIO4 - Manual (Page 17)

3-1
Section 3. Understanding How the
SDM-SIO4 Handles Data
For simple applications the SDM-SIO4 can be configured and controlled from the datalogger
alone, using the datalogger program instruction P113 (CR10X and CR7 dataloggers only).
Future developments will include support for other dataloggers.
More complicated applications require configuration of the SDM-SIO4 using the ‘command
line’ function on a PC running a terminal emulator. This allows you to set up mechanisms to
control the transmission of long, formatted output data and filtering of numerical values out
of received data. This is done by storing the detailed formatting and filtering configurations
in the SDM-SIO4 (see the section about the command line mode below).
Thus when the datalogger needs to send out long or complicated data strings it only needs to
send a short command to the SDM-SIO4 to tell it to do this, i.e. it does not have to pass the
whole string via the SDM interface. Likewise, by telling the SDM-SIO4 how to process
received data, it can strip off the unwanted characters and reduce the data to either binary or
floating point numbers. This minimises the time it takes for the datalogger to get the data and
so allows the datalogger to load the data values into its memory with minimal processing.
3.1 Introduction
For collection of data from an intelligent sensor the datalogger programming is
typically broken down into several steps, which might be:
1. Set up and configure the serial ports, e.g. baud rate, parity, handshaking. This
can be done by one call of the datalogger instruction either at program
compilation (so it is done only once) or perhaps in a subroutine which is called
when a flag is toggled.
2. Use a second call of the instruction to tell the SDM-SIO4 to send out a string
to request data from a sensor and to tell it how to process the returned data.
3. At some point later in the program use a third call to collect the pre-processed
data from the SDM-SIO4.
Before examining the detail of the datalogger instruction it is necessary to
understand the data output formatter and the input filters. These work in principle
(and in certain details) like the formatting and filtering options used to write and
read data from files in some high-level programming languages.
3.1.1 Method of Entering Special / Control Characters
Before going on to discuss filters, you should understand how to enter special /
control characters.
To enter a control character in the range of 0-255 decimal in a filter string,
formatter string or a user string you must use the ‘&hh’ format, where ‘&’ defines
the following two characters, ‘hh’, to be a hexadecimal number between 00 and
FF. For example, ‘&de’ would be character 222 decimal. To use ‘&’ within the
string you must type ‘&&’ (i.e. && = & when in a string).