Campbell SDM-SIO4, Instruction Manual

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Section 1. Introduction
1-4
There is one more buffer, which is used only when the datalogger outputs
floating point data via the SDM-SIO4. This buffer is 241 bytes — long enough
for 60 floating point values. (The size of this buffer is rarely a limitation as it is
emptied quickly.)
1.2.2 SDM Port
This serial port is to connect to the SDM port of the datalogger, e.g. via C1, C2
and C3 on a CR10X. The port is a set of screw terminals marked C1, C2, C3,
I/O, +12 and G. C3 is the Synchronous Device Enable line, C1 is the Data line,
C2 is the Clock line and I/O is a special-purpose Interrupt line.
The Interrupt line can be used with some dataloggers to tell the datalogger to
collect data from the sensor. The SDM-SIO4 pulses the I/O line for 50ms every
250ms if there is data available for the datalogger to collect. This can be used
for sensors which send out data without prompting. For dataloggers which
support interrupt-driven subroutines this can simplify program operation.
The SDM port is used by the datalogger to communicate with the SDM-SIO4
and other SDM peripherals. The speed at which data is transferred is under the
control of the datalogger and this can vary with other activities in the
datalogger and also the length of the SDM cables. The typical transfer speed to
and from the SDM is one byte per millisecond.
Multiple SDM-SIO4s can be connected to the datalogger in parallel with other
SDM-SIO4s or other SDM devices. The only difference would be the SDM
address of each device.
For high-speed communications the SDM cable should be kept as
short as possible and connections made using screened cable.
The cable between the SDM-SIO4 and the datalogger should not
exceed 3m in length.
1.2.3 Case
The case is made of anodized aluminum. It has four slots for 9-way ‘D’
connectors and one slot for the SDM 6-way screw terminals. There is a
momentary push-button switch for command line activation. The size of the
case is 184 x 88 x 34mm. There is a tab at each end to allow for vertical
mounting.
1.2.4 Power Requirements
The SDM-SIO4 has a typical quiescent current consumption of about 0.7mA.
This increases to about 29mA with all 4 ports active. The quiescent state is
entered if there has been no SDM or port activity for approximately 30ms.
The unit can be powered from an unregulated 12V supply (acceptable range 9 -
18V DC).
NOTE