Access each 16-bit word of a 32-bit value with ModbusSimulatorContext

[haxj]

Hi all,

I have some questions regarding the following scenario:

Suppose there's a uint32 value at address addr. From the client, I can access that 32-bit value by sending a Modbus request with address = addr and count = 2. Logically I think the client can also send 2 Modbus requests with count = 1 and address set to addr and addr + 1 to access the high and low word separately.

My questions are:

• I understand that the Modbus specs doesn't officially support 32-bit values, however in the real world, is this scenario common?
• Do real Modbus servers/slaves usually support accessing each word of a 32-bit value separately like this?
• If yes, should the class ModbusSimulatorContext support this kind of access in the future? Currently ModbusSimulatorContext stores the whole 32-bit value at addr without caring about its high/low 16-bit words.

[janiversen]

it does support 32 bit values, if you look more in detail it is stored in 2 addresses (each 16bit).

and it does care about the big/little indian conversion. please remember the modbus protocol always use big indian.

[haxj]

Thanks for your confirmation. I'm using ModbusSimulatorContext but had some issues with this scenario, so I thought there's no support yet. But if it already does, then may be I'm using it wrong or there's a bug.

I'll do some more tests to pinpoint the issues.