Guralp Systems CMG-DM24S12AMS - Manual (Page 57)

CMG-DM24S12AMS Operator's guide
resulting in a data output rate of 200 samples/sec. The following 3 stages
can be set individually for decimation factors of 2, 4, 5, 8, and 10
allowing data to be output at lower rates requiring less storage and
transmission bandwidth. For example, a system can be configured to
provide data at 200, 50, and 10 samples/sec covering the whole of the
seismological broad band range.
The configuration of the DSP is programmable (in the field) via the host
H8 microprocessor. The H8 communicates with the DSP via its high
speed 8-bit ‘host port’, which allows the operating mode/configuration
to be altered and the resulting processed/filtered data to be acquired.
The primary digital interface for the systems is the multiple serial port
card. Each card can contain 1 or 2 dual UARTs (Universal Asynchronous
Receiver Transmitters) and up to 2 cards can be fitted to a SAM/DM
unit. This allows a system with up to 8 serial ports to be configured.
On a DM unit with analogue inputs a serial port is usually configured to
send the data packets to a (local) SAM unit for storage/acquisition or via
a modem or radio link to the central recording station. The second serial
port is available for use with a local GPS receiver for time
synchronisation, or alternatively the first (data) port is used for time
synchronisation from the central station.
The multiple serial port card is usually configured as several data inputs
for a SAM unit allowing it to collect data from up to 8 other SAM or DM
units located locally, using RS232 or RS422 links, or more remotely
using radio links or telephone modems.
Each of the serial ports on a module can be configured for a wide range
of standard baud rates (with different settings available for transmit and
receive channels), allowing a wide range of data links to be used
depending on the required data rates.
The first dual UART supports full modem interface on one port and
hardware handshake on the second. The second dual UART is
configured for data line interface only, supporting software handshake.
Each dual UART is optically isolated to avoid ground loops that could
degrade the performance of the ADC’s. The serial port module includes
32k of RAM for data buffering and formatting by the
transmission/reception process.
March 2004 57