Casella CEL CEL-393 - Manual (Page 61)

these and converting to the necessary conventional mnemonics that are
required on the computer printout.
The sound level meter's internal memory should not be called to its
display when answers are required over the digital interface, and it
should be noted that an eighth answer is available over the interface
when the instrument is configured in the environmental mode. This
provides the period time, and due to the internal architecture of the
instrument it is not available on the instruments display.
The pin out of the interface is shown in Figure 7 whilst the function of the
various pins is shown in Table 6.
The CEL-393B looks at pin 8 only periodically, to determine whether data
is to be output from the CEL-393B, so that if a receiving device changes
this line from being enabled to being disabled, the CEL-393B may still
output a number of further characters before detecting that the serial
output has been switched off.
If the receiver is capable of continuously receiving data at 1200 baud and
has enough time to process this data, then this line can be left enabled.
Otherwise, if the receiver has a 100 byte input buffer, for example, then
this line can be disabled after 75 characters, so that there is room in the
buffer for any bytes sent from the CEL-393B before it has detected that
serial output has been disabled.
It is important to note that the CEL-393B sends at 1200 baud, with each
character represented by 1 start bit, 8 data bits and two stop bits, in the
conventional manner with the least significant bit first.
Each answer is represented by five characters, the first of which is the
code which has its most significant bit set to 1 to allow identification of
the answer set start. It is followed by the hundreds, then tens, then units
and finally the decimal portion of the result. The code for all the data
bytes is ASCII with no parity. The decimal point has to be derived from
the code byte. When an overload occurs, an indication is given by 12
being added to the hundreds byte in the ASCII code.
393 Handbook /57.