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3.2 Using Real-time Data Exchanges
3.2.1 Configuring Real-time Data Exchanges
Real-time data exchanges are used for periodic retrieving data from the connected devices. The
following table shows the parameters that should be configured before enabling a data exchange.
Table 3-3 Real-time Data Exchange Setup
Description Range
Exchange number
0-249
Start device register address
0-65535
Exchange block size, registers
1-114
Device ID
1-247
Polling enabled
1=enabled, 0=disabled
RTC update enabled (optional)
1=enabled, 0=disabled
A data exchange can store from 1 to 114 contiguous 16-bit registers retrieved from a single device. A
block of registers for an exchange is defined by the start register address and the exchange block size.
Refer to Modbus guides for specific devices for available address ranges.
You can individually enable or disable polling data for a specific exchange. If the device has an
onboard real-time clock, you can enable periodic RTC updates from the ETC2002 clock, which may
be synchronizes with the precise satellite GPS clock using an optional IRIG-B input.
Each data exchange utilizes 6 extra registers for time stamping and identification as shown in
Table 3-4, so the actual memory required for one data exchange is 6 + exchange block size. The total
size of all exchanges should not exceed 9000 registers.
Table 3-4 Data Exchange Record
Description Range
Record heading
Record status
0=no data, -1=corrupted record,
1-65534 = device response code
Record time, seconds since 1/1/1970
Record sequence number
0- 65535
Data block (variable size)
Data registers (up to 114)
If data logging is globally enabled in the Data server, the retrieved data is periodically moved from the
data exchange to a log file in the same format, as it is stored in the exchange (see Table 3-4). Each
exchange is provided with a separate data log file.
A data record is always preceded by a status register that indicates whether the data is healthy. Each
record may be identified in a file by a unique 16-bit sequence number that is incremented modulo
65536 with each new record.
3.2.2 Accessing Real-time Data Exchanges
Real-time data exchanges occupy a single continuous block of registers without gaps and are located in
the ETC2002 memory in the address range of 0 to 9000. Since exchanges may have different size, the
location of each exchange in the memory depends on the size of all preceding exchanges. Use the
following formula to define the location of the data exchange:
)
6
Size
Block
Exchange
(
Address
Exchange
1
N
0
n
n
N
+
∑
=
−
=
Note that a location of the exchange in the memory is changed when you change the data exchange
setup, so the previously acquired data would be lost.
