Campbell Scientific CR7 Measurement and Control System - Manual (Page 156)

SECTION 15. I/O CARD ADDRESSING AND MULTIPLE I/O MODULES
15-6
A typical programming example for a CR7
System containing two I/O Modules is given in
the following Program Table. A separate Power
Supply powers the remote I/O Module. The
objective of the programming example is to
conduct a preliminary system check-out by
measuring the battery voltage of the remote
Power Supply and of the power supply powering
the Control Module and I/O Module #1.
PROGRAM
Execution Interval 1 Second
Inst. Param.
Loc. No. Entry Description
1 P 10 Measure Control
Module voltage
1 1 Store result in Input
Loc. 1
2 P 23 Select I/O Module
1 2 I/O Module 2
3 P 10 Measure remote
battery voltage
1 2 Store result in Input
Loc. 2
Any subsequent instructions in the example
would address I/O Module #2 unless Instruction
23 were executed again specifying I/O Module
#1.
15.2.2 SETTING BAUD RATE BETWEEN I/O AND
CONTROL MODULES
The baud rate that data are transmitted
between the Control and I/O Modules is pre-set
to 38.4 k baud at the Factory. This baud rate
can be used for most datalogging applications
provided the distance separating the Control
Module and the I/O Module(s) does not exceed
1,000 ft. Distances in excess of 1,000 ft.
require a slower baud rate setting to
compensate for connector capacitance. Slower
baud rates may limit table Execution Intervals or
throughput rate. Table 15.2-3 lists
recommended baud rates for communicating
with I/O Modules at varying distance from the
Control Module.
TABLE 15.2-3. Recommended Baud Rates
for Remote I/O Modules
Distance Maximum
in Recommended
Feet Baud Rate
0 to 1000 38.4 k baud
1000 to 2000 19.2 k baud
The baud rate is determined by jumper
placement at location S5 of the Control
Module's Serial Interface card (Figure 15.2-1)
and position G7 of the Model 720 I/O Module
Controller card (Figure 15.2-2).
Position S5 has eight pairs of pins. Starting
with the pair nearest to the adjacent board edge
and moving left, baud rates of 1200, 2400,
4800, 9600, 19200, 38400, 76300 or 153600
baud can be selected. The 76.3 and 153.6 k
baud settings are not recommended.
Figure 15.2-2 shows the I/O Module Controller
card. Position G7 has 14 vertically aligned pin
pairs with the 8 uppermost pairs determining
baud rate. A baud rate of 153.6 k baud is
obtained by jumpering the uppermost pair. The
baud rates from the top pair working down are:
153600, 76300, 38400, 19200, 9600, 4800,
2400, and 1200 baud.
Baud rate settings for the Control Module and
the I/O Module(s) must be the same.