Operator`s manual

15 SERIAL INPUT
1. FUNCTION
Instruction 15 for the 21X is used to read data
from an "intelligent" sensor that outputs serial
ASCII data.
- Serial input must consist of one start bit, eight
data bits (eighth bit ignored), no parity, and 1
or more stop bits.
- 1200 baud is the ONLY rate at which the 21X
will accept serial data.
- When Instruction 15 is executed a digital
control port is asserted, signaling the sensor
to send the data. The control port is reset
and the Program Table execution proceeds to
the next instruction when
- the 21X receives a carriage return or
- the number of characters specified in
Parameter 4 are received, or
- the delay time expires (Parameter 5).
- The data line from the sensor to the
datalogger is connected to the high side of a
differential channel (the low side may still be
used as a single ended input).
- Multiple data points can be received per
sensor output. The data point delimiter can
be any character other than a numeric
character, a + or - sign, or decimal. The
delimiter causes data to be stored in the next
consecutive Input location.
2. INSTRUCTION 15 AND PARAMETER
DESCRIPTION
PARAMETERDATA
NUMBER TYPE DESCRIPTION
01: 2 Repetitions
02: 2 Input Channel (differential)
03: 2 Digital Control Port/Logic
Level
X = Port X, TTL logic
1X = Port X, RS232 logic
04: Number of characters per
input
05: 4 Delay time (multiplies of
0.012 sec.)
06: 4 Input location
07: FP Multiplier
08: FP Offset
PARAMETER 1 Repetitions
"Repetitions" specifies the number of sensors to
be read using the same Instruction 15
parameter configuration. For example, a REP
of 3 is used for 3 identical sensors or sensors
that are satisfied by the same parameter
configuration. Instruction 15 must be entered
separately for each sensor or group of sensors
requiring a different configuration.
For each repetition specified, the 21X advances
to the high side of the next differential channel
(parameter 2) and increments to the next
Control Port (parameter 3). The delay
(parameter 5) and number of characters
(Parameter 4) are repeated for each repetition.
PARAMETER 2 Input Channel
The sensor output line is connected to the high
side of the differential channel specified in
Parameter 2.
Standard RS232 logic levels range from 3 to 25
volts and -3 to -25 volts. Voltages in excess of
+8 volts will cause errors and possible
overranging on other analog input channels.
The circuit shown in Figure 1 limits the input
voltage range to 0 to 5 volts. Each input signal
that is out of the +5 volt range requires one of
these circuits or equivalent.
FIGURE 1. Circuit to Limit Input to 0 to 5 volts