Casella CEL CEL-296 - Manual (Page 51)

6. DIGITAL INTERFACE
The CEL low power digital interface is a serial data stream basically
similar to the RS-232C. However, modifications have been made to
reduce the amount of data handled, and minimize the power
consumption. It is designed for direct connection to the CEL-438,
CEL-338, and CEL-238A series of Printer/Loggers, which can
produce hard copies of results, and allows further data reduction to
be performed.
The CEL-433 Serial Interface allows direct connection with other
computer systems by providing an output at RS 232 levels.
A digital output is available for the parameter currently selected on
the sound level meter, the bandwidth and centre frequency chosen
on the filter set, and the level in the band. This output is updated
every 500 milliseconds.
Remote control of the function select and reset lines, and of filter
band stepping enable a complete spectrum to be produced, stored,
and transmitted via the interface.
The CEL-296/3 Filter Set adds six bytes to the serial data stream
generated by the sound level meter. The results are transmitted in
eleven byte data packages as follows.
Byte 1
This contains information to indicate the presence of the six
additional bytes containing frequency information in the format.
BIT
7 6 5 4 3 2 1 0
1 X F X X X X X
Where: 1 = Indication of first byte,
F = Indication that 10 more bytes follow,
X = Sound level meter data if available,
otherwise 0
CEL Instruments Ltd CEL-296/3 Operator Handbook Page 51