Operator`s manual

15 SERIAL INPUT
2
PARAMETER 3 Digital Control Port/Logic Level
This parameter specifies which digital control
port is used and what the input logic level is
(TTL or RS232).
Digital Control Port The digital control port
specified in Parameter 3 is asserted during the
instruction, but is not asserted before or after
the instruction. "Asserted" is 0 volts for TTL
and 5 volts for RS232. "Not asserted" is the
opposite; 5 volts for TTL and 0for RS232. The
control port stays asserted until all data are
received.
NOTE: When the datalogger program is compiled,
all digital control ports are set to 0 volts. Thus,
when programmed to read a TTL input, the
control port is asserted from the time the
datalogger compiles until after the first
execution of Instruction 15.
Logic Level If the input is RS232 logic levels, enter
a 1 before entering the control port number. If
the input to be received is TTL logic levels,
specify only the control port. RS232 logical 1 is
low voltage and TTL is high voltage.
PARAMETER 4 Number of Characters
Parameter 4 specifies the number of characters
per repetition to expect including polarity,
spaces, decimal, alpha, numeric, and carriage
return characters. When the specified number
of characters are received, the 21X advances to
the next repetition or program instruction.
Characters sent after the specified number of
characters are received are ignored. If less are
sent, and a carriage return is received, the
value is stored and the program advances. If
less are sent and a carriage return is not
received and the specified delay expires, -
99999 is stored in the Input location.
PARAMETER 5 Delay
Parameter 5 specifies a time limit for the 21X to
receive characters from the sensor. Units are
0.012 seconds (e.g. entering a delay of 3
causes the 21X to receive characters for a
maximum of 0.036 seconds). When the delay
time expires, the 21X advances to the next
repetition or program instruction. If the delay
expires, -99999 is stored in the Input location
(parameter 6).
PARAMETER 6 Input Location
The Input Location in which the first datapoint is
stored is specified by parameter 6. If more than
one value is received they are placed in
consecutive Input Locations starting with the
specified location.
3. EXAMPLE: INSTRUCTION 15 AND
THE AIR-DB-1A BAROMETER
This example shows how to use a 21X with
Instruction 15 to read the AIR-DB-1A
Barometer. Various barometer functions
(mode, units of output, baud rate, etc.) are
determined by jumpers internal to the
barometer. A summary of the jumper
configurations is found in Appendix A. Please
refer to the AIR barometer manual for jumper
configuration details.
3.1 21X/BAROMETER CONFIGURATION
LIMITATIONS
The 21X is limited to reading only certain
barometer jumper configurations as described
below:
- MODES of OPERATION The 21X reads
all barometer "Modes of Operation" that
have serial output except the Serial ID
and Signature Analysis portion of the
Test Mode. The 21X will NOT read a
parallel input.
- UNITS of OUTPUT The 21X reads all
"Units of Output".
- NUMBER of MEASUREMENTS
AVERAGED Any "measurements
averaged" barometer option may be
read by the 21X. Keep in mind that the
greater the number of measurements
used to compute an average, the longer
it takes for Instruction 15 to execute,
resulting in a greater current drain (25
mA).
- BAUD RATE 1200 baud is the ONLY rate
at which the 21X accepts serial data.
- RS232 JUMPERS For typical field use
where power is limited, the RS232
jumpers should be removed to enable a
TTL (0-5v) level output.