Campbell Scientific AM16/32A Multiplexer - Manual (Page 17)

AM16/32A Relay Analog Multiplexer
5.1 Single Loop Instruction Sequence
When a number of similar sensors are multiplexed and measured, the
Instructions to clock the AM16/32A and to measure the sensors are placed
within a program loop. For the CR23X, CR10(X), 21X, and CR7, the
generalized structure of a program loop is as follows:
TABLE 2. Single Loop Instruction Sequence
# INSTRUCTION FUNCTION
1 Set port high to activate AM16/32A
2 Begin loop
3 Clock AM16/32A & delay
4 Step loop index
(required in some configurations)
5 Measure sensor
6 Additional processing
7 End loop
8 Additional program loops
9 Set port low to deactivate AM16/32A
#1, #9 Activate/deactivate the AM16/32A −The control port connected to
reset (RES) is set high to activate the AM16/32A prior to the advance and
measure sequence and set low following the measurement loop(s). For the
CR10X, CR23X, and CR10, 21X, CR7 dataloggers with OS series PROMs,
use instruction 86 to set and reset the port (for CR10, 21X, and CR7 with
earlier PROMs, use Instruction 20).
#2, #7 Begin and End a Loop − For the CR23X, CR10(X), 21X, and CR7
dataloggers, a loop is defined by Instruction 87 (Begin Loop), and by
Instruction 95 (End). Within Instruction 87, the 2nd parameter (iteration
count) defines the number of times the instructions within the loop are
executed before the program exits the loop.
# 3 Clock and Delay − With the CR23X and CR10(X) the clock line is
connected to a control port. Instruction 86 with the pulse port command (71-
78) pulses the clock line high for 10 ms. Instruction 22 can be added
following the P86 to delay an additional 10 ms.
When using a 21X or CR7, the clock line may be connected to either an
excitation or control port. Connection to an excitation port is preferred
because only one instruction (22) is required to send the clock pulse.
Instruction 22 should be configured to provide a 10ms delay with 5000 mV of
excitation. A control port can be used to clock the AM16/32A if an excitation
port is not available. The 21X and CR7 instruction sequence required to clock
with a control port is: Instruction 20 (set port high), Instruction 22 (delay 20
ms without excitation), followed by Instruction 20 (set port low).
# 4 Step Loop Index – With the CR23X, CR10(X), 21X or CR7, the Step Loop
Index instruction “90” is used when a measurement instruction within a loop
has more than one repetition. This instruction allows 2 - 4 sensors per SET to
be measured by 2 – 4 analog input channels. The Step Loop Index instruction
sends each measurement value to a sequentially assigned input location
without overwriting any other current iteration value. Without this instruction,
the input location within the loop will advance by only one location per loop
iteration even though the measurement instruction’s Input Location is indexed.
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