Obvius A8911-23 - Manual (Page 9)

Register Functions
Pulse Count: The pulse count is stored as an unsigned 32bit integer. This allows for 2^32 pulses (4.2billion) to be counted
before rollover. On Modbus systems that do not allow you to read 32bit values, you can calculate the pulse count as follows:
count = (MSW * 65536) + LSW
or
count = (MSW << 16) | LSW [bit shift high order word by 16 bits and xor against low order word ]
Pulse count registers accumulate a total number of pulses received on each pulse input. The pulse count totals always
increment and can not be cleared or set to an arbitrary value to prevent tampering. All pulse count totals are stored in non-
volatile memory to preserve counts during power failure. The unsigned 32 bit counter values can accumulate up to 4.29
billion (2^32) pulses before rollover.
All 32 bit data point values are encoded in 2 Modbus registers (16bits each). Modbus master systems should always query
the A8332-8F2D using a single query to read an entire block of registers. Never use two queries to read one register and
then combine the two results into a single 32 bit value. Doing so will allow the pulse count to increment in the middle of the
two Modbus queries, and will cause intermittent data readings that are incorrect.
For example, a pulse input has a count of 65534. This is represented as a 32 bit hex number 0x0000FFFE. The first 4 digits
are the MSW register, the second 4 digits are the LSW register. The Modbus Master reads the first (MSW) register and gets
0x0000. In between the two readings, the pulse input counts 2 more pulses, making the total 65536 or 0x00010000 in hex.
Next the Master reads the second (LSW) register and gets 0x0000. When the two registers are combined, the result is
0x00000000. The proper way to handle this situation is to simply read both registers in a single Modbus query.
Page 9 A8911-23