7 DEVICE SUPPORT BLOCK (DSB)
7.2 About DPV1 read/write messages configuration in DSBs
DSB blocks can be configured to support the DPV1 data record read/write between PROFIBUS master and
slaves. For each slave device, the DPV1 configuration can be done in the respective DSB blocks. In addition,
the following parameters can be configured in the DSB blocks to control the DPV1 requests from multiple
Number of DPV1 data records (DPV1NUMPOLL)
Scan priority (DPV1PRIORITY)
Scan ratio of high and low priority requests (DPV1NUMHIGHPRIREQ)
The DPV1 write is always considered as high priority request compared to the DPV1 read.
The following DSB blocks supports a maximum number of 16 DPV1 data access requests from data records.
However, the GENIODSB supports 64 data access requests from data records.
You must read the PROFIBUS slave vendor manual before configuring the DPV1 requests in the DSB block.
A DPV1 record can be parsed to 16 data fields (parameters/data types). If a DPV1 data record needs to be
parsed to more than 16 fields, then the
same record can be configured multiple times for read or write and parsed to more fields, or
C300 strategies can be used to parse the complex record into simpler records.
DPV1 data write occurs in three stages as follows:
1. Read the DPV1 data from the PROFIBUS-DP device
2. Append the modified DPV1 value
3. Write the modified value to the PROFIBUS-DP device
DPV1 records scanning
Generally, all the DPV1 requests (16 for all DPV1 supported DSBs and 64 for GENIODSB) in DSB are
scanned in a cyclic manner irrespective of the DPV1 request configuration.
One DPV1 scan cycle has 16 time slots. Therefore, all the DPV1 request (even if it is not configured) is scanned
once in every cycle. For example, consider that the time slot is 1 second and there are four DPV1 requests that
are configured. In this scenario, the first DPV1 request is scanned at n, n+16, n+32, and so on.
The Scan Priority (DPV1PRIORITY) has the following options that are used for scanning the DPV1 requests.
When the DPV1PRIORITY parameter is set as "High," DPV1 requests are polled for every cycle.
When the DPV1PRIORITY parameter is set as "Low," the DPV1 requests are polled based on the
DPV1NUMHIGHPRIOREQ parameter. For example, if the DPV1NUMHIGHPRIOREQ parameter is set as 5,
then the "Low" requests are polled once for every 5 cycles.