Campbell SDM-IO16A User manual

09/2020
Copyright © 2020
Campbell Scientific, Inc.

Table of contents
1. Introduction 1
2. Specifications 2
2.1 General 2
2.2 Terminal specifications (output mode) 3
2.3 Terminal specifications (input mode) 3
2.4 Pulse counting specifications 4
3. Installation 6
3.1 Power considerations 6
3.2 Terminal connections 7
3.3 Address selection switches 8
4. Programming the data logger 10
4.1 General principles 10
4.2 SDMIO16() instruction 11
4.3 SDMCD16AC() instruction 13
4.4 SDMSpeed() instruction 14
4.5 Command codes for the SDMIO16() instruction 14
Appendix A. General principles of pulse and frequency measurements 20
A.1 Introduction 20
A.2 Frequency and duty cycle measurement range 20
A.3 Resolution of frequency measurements 21
A.4 Resolution of duty cycle measurements 21
A.5 Debounce filtering 22
A.6 Using the I/O line to trigger code to run on a data logger 23
Table of Contents - i

1. Introduction
The SDM-IO16A expands the digital input and output capability of Campbell Scientific data
loggers. It offers similar functionality to the control terminals of Campbell Scientific data loggers.
The SDM-IO16A (see FIGURE 1-1 (p. 2)) is a synchronously addressed peripheral. It has 16
input/output (I/O) terminals configurable for input or output which expand the number of
control terminals of the data logger. It is fully compatible with Campbell Scientific GRANITE-
series, CR6, CR3000, CR1000X, CR800-series, and CR1000 data loggers.
NOTE:
This manual provides information only for current CRBasic data loggers. For retired CRBasic
and Edlog data logger support, see a prior SDM-IO16 manual at
www.campbellsci.com/manuals.
When a terminal is configured as an input, it measures the logical state of the terminal, counts
pulses, measures the frequency of and determines the duty cycle of signals applied to the
terminal. In pulse counting mode there is also an option to enable switch debounce filtering so
the unit will accurately count switch closure events. The SDM-IO16A measures the frequency of
signals by measuring the time between pulses, thereby giving relatively high-resolution
measurements even for low frequency signals.
The module may also be programmed to generate a signal to the data logger when one or more
input signals change state, which can be used to trigger special code in the data logger. This is
known as an interrupt function, as it is similar to a technique supported in microprocessors.
When configured as an output, each terminal is set to 0 or 5V by the data logger. In addition to
being able to drive normal logic level inputs, when an output is set HIGH a ‘boost’ circuit allows
it to source a current of up to 133 mA (short-circuited to ground) at a reduced output voltage,
allowing direct control of low voltage valves, relays, or other components. Refer to graph (d)
Output voltage versus current output in FIGURE 2-1 (p. 5) to see the available current at different
voltages.
The SDM-IO16A is a synchronously addressed data logger peripheral. Data logger control
terminals 1, 2 and 3 are used to address the SDM-IO16A and exchange digital data with it. This
module uses advanced error checking techniques to ensure correct transmission of data to and
from the module. Up to fifteen SDM-IO16As may be addressed, making it possible to control a
maximum of 240 terminals from the first three data logger control terminals.
SDM-IO16A 16-Channel Input/Output Expansion Module 1

FIGURE 1-1. SDM-IO16A
2. Specifications
2.1 General
Compatible data loggers: GRANITE series, CR6, CR3000, CR1000X, CR800 series, and CR1000
Operating voltage: 12 VDC nominal (9 to 18 V)
Current drain at 12VDC: 600 µA typical standby (all terminals HIGH, no load, not pulse
counting)
Maximum (no output load): 3mA active with all 16 terminals
counting pulses at 2 KHz. Above the standby level, power
consumption is roughly proportional to input signal frequency and
number of terminals used. Maximum 4.5mA in high-speed mode
with 1-16 terminals counting pulses from 0Hz to 8KHz.
Current drawn from any output must be added to the standby level
to give the total current drain.
SDM port: 0/5 V logic level port compliant with the requirements of the
Campbell Scientific SDM protocol — this is designed for
connection to the data logger SDM port.
SDM-IO16A 16-Channel Input/Output Expansion Module 2

Operating temperature: –40 to 70 °C standard
Size: 188 x 64 x 22 mm (7.4 x 2.5 x 0.9 in)
Mounting: Mounting brackets have two holes at 177.8mm (7in) nominal
spacing. Mounting screws and plastic inserts suitable for use with
Campbell Scientific enclosures are also supplied.
Weight: 175 g (6.2 oz)
EMC status: Complies with EN61326:2013
Total SDM cable length: 6 m (20 ft) maximum recommended
2.2 Terminal specifications (output mode)
Output voltage (no load): Output ON/HIGH, nominal 5 V (minimum 4.5 V)
Output OFF/LOW, nominal 0 V (maximum 0.1 V)
Output sink current: Output will sink 8.6 mA from a 5 V source1
Output source current: Output will source 42 mA @ 3 V, 133 mA short-circuited to ground1
Max. output current:
(total for all outputs)
Limited by the 12 V supply.
2.3 Terminal specifications (input mode)
Input voltage: Input high, 4.0 V minimum threshold
Input low, 1.0 V maximum threshold
All inputs feature Schmitt triggered detectors.
Input protection: The input is clamped at –0.6V and +5.6V relative to ground via a
33Ω resistor1. This will withstand a continuous current flow of
200mA (including that which might be caused by accidentally
connecting directly to a 12V supply). To limit power dissipation and
damage at higher voltages than 12V, an external series current
limiting resistor is recommended.
Input impedance: The input is biased to +5 V relative to ground by a 100 kΩ resistor.
SDM-IO16A 16-Channel Input/Output Expansion Module 3

2.4 Pulse counting specifications
Maximum frequency: Low-speed mode 2.048KHz on all channels simultaneously with
switch debounce-mode set off, with a 50/50 duty cycle.
150Hz on all channels with default switch debounce timing
enabled and a 50/50 duty cycle2.
High-speed mode 8.192KHz on all channels simultaneously with
switch debounce-mode set off with a 50/50 duty cycle.
Minimum frequency: A frequency of 0Hz is measured if there are less than two high-to-
low signal transitions in the measurement interval.
Minimum pulse width: A pulse must stay high or low for a minimum of 244 μs (low-speed
mode) and 61.04 μs (high-speed mode) for a change of state or
pulse to be counted.
Switch debounce timing: With the default settings, a switch between the input and G must
remain closed for 3.17ms and then remain open for 3.17ms, to be
counted as a closure. The debounce is changeable from the user
program. In high-speed mode the debounce timing is one quarter
of this at 0.7925ms.
Accuracy: Internal clock accuracy ±0.01% (worst case) over the standard
temperature range of –40 to 70°C.2
Duty cycle resolution: Depends on frequency and measurement interval.2The average
duty cycle is measured for signals up to 4kHz (low-speed mode)
and 16KHz (high-speed mode).
Max measurement interval: For frequency or duty cycle measurements the data logger must
request a measurement at an interval no longer than 4096 seconds
(low-speed mode) and 1024 seconds (high-speed mode). Each
channel is measurable at different intervals, both for frequency and
duty cycle.
1If more detailed input/output characteristics are required, experienced users should consult the equivalent circuit
diagrams and graphs shown in FIGURE 2-1 (p. 5).
2See General principles of pulse and frequency measurements (p. 20) for a more detailed discussion.
SDM-IO16A 16-Channel Input/Output Expansion Module 4

(a) Input biasing and protection
(b) Output set ON (c) Output set OFF
(d) Output voltage versus current output
(e) Output voltage versus resistive load
FIGURE 2-1. Simplified equivalent terminal circuits and graphs of output voltage
SDM-IO16A 16-Channel Input/Output Expansion Module 5

3. Installation
For correct operation, the SDM-IO16A must be installed where there is no risk of water ingress or
condensation.
WARNING:
The order in which connections are made is critical. Always connect 12V first, followed by
ground, then the SDM control terminals.
The CABLE5CBL-L or a similar cable connects the data logger to the SDM-IO16A. For data logger
connections, see Table 3-1 (p. 6). Refer to FIGURE 3-2 (p. 8) for details of how to use the spring-
loaded terminals.
Table 3-1: Data logger to SDM-IO16A connections
Connection order SDM-IO16A Data logger
First 12 V 12 V on data logger or
external supply
Second ⏚G
Third
C1
C2
C3
C1
C2
C3
When using multiple SDM-IO16As, each SDM-IO16A is wired in parallel by connecting the data
logger connections of one SDM-IO16A to the next.
The transient protection of the SDM-IO16A relies on a low resistance path to earth. Ensure that
the ground return wire has as low a resistance as possible.
NOTE:
The total cable length connecting SDM-IO16As to SDM-IO16As and the data logger must not
exceed 6m (20ft). Total cable lengths in excess of 6m (20ft) will adversely affect
communications between the module and data logger.
3.1 Power considerations
For most applications, especially for pulse counting or status inputs, the data logger supply is
used to power the SDM-IO16A, as shown in FIGURE 3-1 (p. 7) (a).
SDM-IO16A 16-Channel Input/Output Expansion Module 6

When being used for control and outputting current the SDM-IO16A power requirements will be
large compared to most Campbell Scientific products when driving significant loads. For this type
of application an external power supply, as shown in FIGURE 3-1 (p. 7) (b), is recommended to
power the SDM-IO16A.
(a) Connection with data logger supply
(b) Connection with external supply
FIGURE 3-1. Connection block diagrams
3.2 Terminal connections
The SDM-IO16A uses spring-loaded terminals for each connection, which provide quick,
vibration resistant connections. The I/O terminals are labeled 1 to 16. A common ground terminal
is provided between each pair of I/O terminals.
Strip any insulation from the wire to give 7 to 9mm bare wire. Use a screwdriver to push against
the orange lever to open the terminal contact in either the top or front slot, as appropriate. Push
the wire into the opening, and, while holding it in position, release the screwdriver to close the
terminal contact. The wire will now be firmly held in place. See FIGURE 3-2 (p. 8).
SDM-IO16A 16-Channel Input/Output Expansion Module 7

NOTE:
It is not possible to reliably insert more than one solid-core wire into one terminal connector
unless the wires are soldered or clamped together. When inserting more than one stranded
wire, twist the bare ends together before insertion.
FIGURE 3-2. Use of terminal blocks
3.3 Address selection switches
Each SDM module must have a unique address. Address 15 (switch setting F) is reserved for the
SDMTrigger() instruction. The factory-set address is 00. Table 3-2 (p. 8) shows switch position
and the corresponding address. FIGURE 3-3 (p. 9) shows the position of the switch.
Table 3-2: SDM-IO16A SDM address settings
Switch Setting Decimal Address Base 4 Address
0 0 00
1 1 01
2 2 02
3 3 03
4 4 10
5 5 11
6 6 12
7 7 13
8 8 20
SDM-IO16A 16-Channel Input/Output Expansion Module 8

Table 3-2: SDM-IO16A SDM address settings
Switch Setting Decimal Address Base 4 Address
9 9 21
A 10 22
B 11 23
C 12 30
D 13 31
E 14 32
F (reserved) 15 33
FIGURE 3-3. Address selection switch
Each SDM-IO16A must be set to a unique address on the SDM bus, so no two SDM peripherals
share the same address.
SDM-IO16A 16-Channel Input/Output Expansion Module 9

4. Programming the data
logger
4.1 General principles
The SDMIO16() instruction is used to control operation and configure each I/O terminal of the
SDM-IO16A. The different variants of this instruction are described in SDMIO16() instruction (p.
11).
The general form of the instruction specific to the SDM-IO16A includes:
lParameters to specify which module to address
lA command code to specify what the module is to do
lControl parameters and pointers to input locations/variables which hold data (either read
by the module or used to control the outputs of the module)
The instruction differs from many others in that, rather than addressing a variable number of
terminals (using a repetitions parameter), terminals are dealt with in blocks of 1, 4, 8 or 16
terminals at a time. The specific terminal(s) and number to be controlled is implicit in the
command code used. This improves the efficiency of programming and reduces the amount of
data transferred between the module and data logger via the SDM port.
The module is reconfigured from the controlling program to allow for more demanding
applications. In most cases, though, on power-up the I/O terminals of the SDM-IO16A default to
input mode, with no switch debounce filtering and measurement of frequency and duty cycle
automatically starts for all terminals.
For many input measurements, the controlling program in the data logger is written to ask the
SDM-IO16A for measurements of status, duty cycle, or frequency from any channel. The only
constraint is it must ask for duty cycle or frequency measurements more frequently than once
every 4096 seconds (low-speed mode) and 1024 seconds (high-speed mode) (see General
principles of pulse and frequency measurements (p. 20)).
Where one or more terminals will be used for output, one call of the instruction within the
normal program structure is used to set those terminals to either a fixed state, or a state
dependent upon a variable.
SDM-IO16A 16-Channel Input/Output Expansion Module 10

An instruction is typically included to configure the SDM-IO16A before it is used. Conditions
when configuration is needed include:
lWhere terminals are used as switch closure inputs (program example 6)
lWhere a terminal change of state is used to toggle the I/O line, normally to generate an
interrupt to the data logger (program example 7)
lWhere the terminal is used as a fixed output (program examples 1 and 2)
See the SDM-IO16A program example on the Campbell Scientific website:
www.campbellsci.com/downloads/sdm-io16a-program-example.
The configuration of individual terminals is also changed during normal program operation, if
required.
4.2 SDMIO16() instruction
The SDMIO16() instruction in CRBasic supports all the functions of the SDM-IO16A. An example
program for the SDM-IO16A using the SDMIO16() instruction is found on the Campbell
Scientific website: www.campbellsci.com/downloads/sdm-io16a-program-example. This program
demonstrates multiple ways to configure the SDM-IO16A for input and output using the
SDMIO16() instruction.
Syntax
SDMIO16 (Destination, IO16Status, SDMAddress, IO16Cmd, Mode16_13, Mode12_9, Mode8_
5, Mode4_1, Multiplier, Offset)
Remarks
The terminals on the SDM-IO16A are configured for either input or output. When configured as
input, the SDM-IO16A measures the logical state of each terminal, counts pulses, and measures
the frequency of and determines the duty cycle of applied signals. It is also possible to make the
SDM-IO16A generate an interrupt signal to the data logger when one or more input signals
change state. When configured as an output, each terminal is set to 0 or 5V by the data logger.
In addition to being able to drive normal logic level inputs, when an output is set high a ‘boost’
circuit allows it to source a current of up to 133mA (short-circuited to ground), allowing direct
control of low voltage valves, relays, or other components. Refer to graph (d) Output voltage
versus current output in FIGURE 2-1 (p. 5) to see the available current at different voltages.
SDM-IO16A 16-Channel Input/Output Expansion Module 11

Destination This parameter is a variable or variable array in which to store the results of
the measurement (command codes 1 - 69, 91, 92, 99) or the source value
for the command codes (70 - 85, 93 - 98). The variable array for this
parameter must be dimensioned to accommodate the number of values
returned (or sent) by the instruction.
IO16Status This parameter is used to hold the result of the command issued by the
instruction. If the command is successful a 0 is returned; otherwise, the
value is incremented by 1 with each failure.
SDMAddress This parameter defines the address of the SDM-IO16A with which to
communicate. Valid SDM addresses are 0 through 14. Address 15 is
reserved for the SDMTrigger instruction.
IO16Cmd This parameter is used to set up the SDM-IO16A. See Command codes for
the SDMIO16() instruction (p. 14) for a detailed description of the
command codes.
SDM-IO16A 16-Channel Input/Output Expansion Module 12

Mode Each Mode parameter is used to configure a bank of four terminals when
a command code 86 through 90 is used (if any other command code is
used, enter 0 for the Mode parameters). Mode is entered as a four-digit
parameter, where each parameter indicates the setting for a terminal.
Terminals are represented from the highest terminal number to the lowest,
from left to right (e.g., 16 15 14 13; 12 11 10 9; 8 7 6 5; 4 3 2 1). There are
Modes for terminals 16 to 13, 12 to 9, 8 to 5, and 4 to 1. The valid codes are:
Code Description
0 Output logic low
1 Output logic high
2 Input digital, no debounce filter
3 Input switch closure 3.17 ms (low-speed mode) and 0.7925 ms
(high-speed mode) debounce filter
4 Input digital interrupt1enabled, no debounce filter
5 Input switch closure interrupt1enabled 3.17 ms (low-speed
mode) and 0.7925 ms (high-speed mode), debounce filter
6 Undefined
7 Undefined
8 Undefined
9 No change
Multiplier,
Offset
The Multiplier and Offset parameters are each a constant, variable, array,
or expression by which to scale the results of the measurement.
1Refer to Using the I/O line to trigger code to run on a data logger (p. 23) for more information on the interrupt
function.
4.3 SDMCD16AC() instruction
All but the oldest versions of the CR5000 operating system also support the SDMCD16AC()
instruction to control the SDM-IO16A for output mode only. This instruction should only be used
if backward compatibility is required, as only SDMIO16() supports error detection on
communications between the module and the data logger.
See the CRBasic Help for more information on this instruction.
SDM-IO16A 16-Channel Input/Output Expansion Module 13

NOTE:
This cannot be mixed with the SDMIO16() instruction in the same program.
4.4 SDMSpeed() instruction
The SDMSpeed() instruction is used to change the bit period that the data logger uses to clock
the SDM data. Slowing down the clock rate may be necessary when if data transmissions are
impaired. Typically, this will only occur when the total length of the cables connecting the data
logger and SDM devices is approaching the maximum of 6m (20ft).
Syntax
SDMSpeed (BitPeriod)
The BitPeriod parameter is either an integer or a variable. If the SDMSpeed() instruction is
not in the program, a default bit period is used. If no BitPeriod is specified, the minimum
allowable bit period is used. The following table shows the default, minimum allowable, and
maximum bit period for each CRBasic data logger.
Table 4-1: Bit period values
Data logger Default bit period
Minimum
allowable bit
period
Maximum bit
period Resolution
GRANITE series,
CR6, CR3000,
CR1000X
28.80 μsec 10 μsec 1 msec 4.3 μsec
CR1000,
CR800 series 26.04 μs 9 μs 2 ms 8.68 μsec
4.5 Command codes for the SDMIO16()
instruction
There are approximately one hundred command codes for the IO16Cmd parameter in the
SDMIO16() instruction. See CRBasic Help for the full list of command codes. Each type of
action is generally possible for either a single or block of terminals of various sizes, as discussed
in General principles (p. 10). A summary table of common command codes is shown in Table 4-2
(p. 18). The small number of different types of action allows the commands to be grouped:
SDM-IO16A 16-Channel Input/Output Expansion Module 14

Pulse counting (1 to 23): Reads the counts accumulated on the specified terminals
since they were last read. The maximum number of
counts possible is 65535. If the count has not been read
before this maximum is reached, this figure will roll over
(from 65535 back to 0) at this point. The count is
incremented when there is a low to high transition on
the terminal.
Frequency measurement (24 to 46): Reads the average frequency on specified terminals since
the last time a frequency command was called. See
General principles of pulse and frequency measurements
(p. 20) for a full discussion of the effects of sample rate
on frequency of measurement. Generally, the longer the
sample rate the higher the resolution. However, the
interval between frequency commands for any one
terminal must be less than 4096 seconds (low-speed
mode) and 1024 seconds (high-speed mode).
Duty cycle measurement (47 to 69): Reads the average duty cycle on the specified terminals
since the last duty cycle command for that terminal. See
General principles of pulse and frequency measurements
(p. 20) for a full discussion of the effects of sample rate
on duty cycle measurement. Generally, the longer the
sample rate the higher the resolution. However, the
interval between duty cycle commands for any one
terminal must be less than 4096 seconds (low-speed
mode) and 1024 seconds (high-speed mode). The value
output is a number between 0 and 100 that indicates the
percentage of time the terminal was high.
SDM-IO16A 16-Channel Input/Output Expansion Module 15

Set the terminal debounce time (70 to
85):
Sets the debounce filtering time in multiples of 244 μs
(low-speed mode) and 61.04 μs (high-speed mode) from
0 to 65535 on the specified terminal. On power-up, the
default time parameter is set to 0, i.e. no debounce
filtering. If debounce filtering is enabled using one of
the command codes 86 to 90, this parameter is set to 12,
equivalent to a filter time of 3.17 ms (low-speed mode)
and 0.7925 ms (high-speed mode). See General
principles of pulse and frequency measurements (p. 20)
for full details of the operation of this filter and the
timing.
Configure the terminals (86 to 90): Sets the configuration of each terminal using the Mode
parameter set from 2 to 5, forming part of the
instruction. The options allow setting of output state or
input filtering and whether a terminal will cause the I/O
line to generate an interrupt pulse to the data logger.
Read the terminal states (91 to 92): Reads the state of all the terminals into either one or 16
sequential variables. For normal logic input a value of 0
is returned for the low state and a value of 1 is returned
for the high state, while for switch closures 0 and 1 relate
to closed and open. The current state of all terminals is
read, even if some are being used for outputs or
frequency inputs.
Set the terminal states (93 to 94): Sets the pattern of the terminal output state, either from
a single location or 16 sequential locations. These
commands will only change the state of terminals
already set to output (using one of the command codes
86 to 90, 95 or 96). The pattern is stored internally, so if a
terminal is subsequently changed from input to output
(using command code 95 or 96) the terminal will then
change to match that set by an earlier call with
command code 93 or 94.
Set the direction (input or output) of
the terminals (95 to 96):
Sets the direction of the terminals either from a single
location or 16 sequential locations. A value of 1 for a
terminal sets it to input and a value of 0 sets it to output.
On power-up, terminals default to being inputs. If the
direction is set to be an output immediately after power-
up the state will be low.
SDM-IO16A 16-Channel Input/Output Expansion Module 16

Set the interrupt mask (97 to 98): Sets a binary mask across the terminals to define
whether a change of state on the terminal (which must
also be configured as an input) will generate an
interrupt signal to the data logger. When the
appropriate mask bit representing the terminal is set to 1
an interrupt will be generated whenever the terminal
changes state. Please refer to Using the I/O line to
trigger code to run on a data logger (p. 23) for more
details of this function.
Read module status (99): Reads back the module operating system signature
(which is calculated once at power-up), a number which
identifies the operating system version plus two
counters. These are a watchdog error counter which is
incremented if the module crashes because of a software
or hardware failure that required the SDM-IO16A to be
reset and a communications error counter which
represents the number of times SDM communications
between the data logger and SDM-IO16A failed. Both
counters have a maximum limit of 255 counts and are
reset to zero when this command code is used to read
them. This command is only normally used when trying
to diagnose problems with the data logging system.
Set low-speed mode (103): Sets low-speed mode 4096 Hz sample rate (this is the
default at power up).
Set high-speed mode (104): Sets high-speed mode 16384 Hz sample rate. This should
be executed every scan in case of power failure.
SDM-IO16A 16-Channel Input/Output Expansion Module 17

Table 4-2: Common command codes (in italics) relative to terminal number and function
Terminal numbers
Action
Terminal
block
size
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
Read
counts 11 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
417 18 19 20
821 22
16 23
Read
frequency 124 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39
440 41 42 43
844 45
16 46
Read
duty
cycle
147 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62
463 64 65 66
867 68
16 69
Set
debounce 170 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85
Set-up
terminals 489 88 87 86
16 90
Read
state 16 91 or 92
Set
state 16 93 or 94
SDM-IO16A 16-Channel Input/Output Expansion Module 18