Campbell Scientific SDM-SIO4 4-Channel Serial I/O Interface - Manual (Page 9)

Section 1. Introduction
1-3
1.2 Specifications
1.2.1 Serial Ports
The SDM-SIO4 has four serial ports which can be configured independently to
use different serial data formats and baud rates (from 25 to 115,200 baud).
These ports are 0-5V logic or ±5V for RS232 and are configured similar to a
PC ‘AT’ style DTE serial port.
Handshaking, to control the flow of data to and from a sensor, can be done by
the datalogger or SDM-SIO4 if needed, and can be in the form of hardware or
software protocols.
TABLE 1-1. SDM-SIO4 Serial Port Pin Configuration
Pin No. SDM-SIO4 Port
1. RI ring indicate/DCD in
2. RX in
3. TX out
4. DTR data terminal ready out
5. Ground
6. DSR in
7. RTS request to send out
8. CTS clear to send in
9. +5V if internal link fitted, otherwise no connection
If you have an older SDM-SIO4 which has female ‘D’ type
connectors, your connections will be different from those shown
above. Please either refer to your earlier Manual or contact
Campbell Scientific for further details.
Serial Port Buffers
Each serial port has a receive (Rx) buffer, a transmit (Tx) buffer and a
processed data storage buffer. It is important to understand these buffers as
their size can determine how often data must be collected from the SDM-SIO4
by the datalogger. It is important to avoid letting these buffers fill up. They are
of the ‘fill and stop’ type, i.e. if they fill up, and more data is sent into the
buffer, the extra data will be lost.
The receive and transmit buffers for each port are 981 bytes long and there is
an additional 16-byte hardware buffer for each port.
The processed data storage buffer (used to store converted data ready for the
datalogger to collect) is 891 bytes long, which is large enough for 222 4-byte
Campbell Scientific floating point values (refer to the datalogger manual for
more details of this format).
NOTE