While setting up communication between Yokogawa Centum CS300 and Bently 3500/92 Comm gateway module, i am not able to get correct values of the analog data from holding resisters. Whereas the status data (digital), i.e, alarm or trip states are received without any issues.

Communication settings in the slave i.e 3500/92 are as below,
Full Scale Data Range: 4095
Baud Rate: 9600
Parity: Even
Stop Bits: One
Byte Timeout: 3 Byte
Numeric Format: Hexadecimal
Word Swapped: Enabled

What could possibly be the error on the Yokogawa settings? For redundancy purposes, Two parallel serial links of RS485 are used with two slave devices on each link. Slave addresses are kept identical on both the links i.e 1&2.

Appreciate a quick response.

 

1. Parity is redundant with CRC checking, so you might disable parity else you may limit full register resolution of 0-65535.

2. It maybe that you are scaling a register that should be read directly.

3. A holding register is not normally used to pass an analog input, an input register is used for analog inputs. Holding registers can be read from or written to, an input register can only be read from by the host.

4. Registers can have a 16 bit value, 0 to 65535, it would make no real sense to scale it back to 4095 even if scaling were used, else,

5. I suspect your analog signal has a A/D range of 0 to 4095 representing a 4-20 mA circuit, so an input register might have 800 for 4 mA and 4000 for 20 mA which is 0-100% EUs.

6. Make sure you try swapping both ways.

These are some of the possible issues to explain the situation. A protocol analyzer tool would be the quickest way to sort out the problem.

 

Parity adds a bit to check whether or not a serial word (byte) passes the test of having an even or odd number of bits set in the word. Parity bits are handled by a UART and are not part of the byte an application program transmits or receives as data. A CRC acts on an entire message. Parity checking may be unwarranted with a CRC, but it is not redundant. Parity has absolutely nothing to do the "full register resolution" of a word or any size data stream send or received over a serial link.