Register Functions - Leviton A8911 Manual De Instalación Y Funcionamiento

8 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
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 A8911-23 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.
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.
[bit shift high order word by 16 bits and xor against low order word]
10