Confusion with Bitwise operators for Modbus

[ak_duino]

I am trying to understand what exactly what this function is doing.
This is a code for Modbus communication.
I recognize that the user is trying to write to several holding registers ie
modbusTCPClient.wrtie(16). The 16 being a function code for write to multiple registers.
anyways if someone could help me decifer the operators on the
modbusTCPClient.write( address & 0xFF );
modbusTCPClient.write( dataLen >> 8 );
modbusTCPClient.write( dataLen & 0xFF );
modbusTCPClient.write( dataLen * 2 );
for ( byte i = 0; i < dataLen; i++ ) {
modbusTCPClient.write( data[i] >> 8 );
modbusTCPClient.write( data[i] & 0xFF );

that would be great.
the function is called in the code as

uint16_t data[5];
writeMulti(2,0x40000,data,5)

void writeMulti( uint8_t id, uint8_t address, uint16_t *data, uint8_t dataLen ) {
  modbusTCPClient.write( id );
  modbusTCPClient.write( 16 );
  modbusTCPClient.write( address >> 8 );
  modbusTCPClient.write( address & 0xFF );
  modbusTCPClient.write( dataLen >> 8 );
  modbusTCPClient.write( dataLen & 0xFF );
  modbusTCPClient.write( dataLen * 2 );
  for ( byte i = 0; i < dataLen; i++ ) {
    modbusTCPClient.write( data[i] >> 8 );
    modbusTCPClient.write( data[i] & 0xFF );
    //vTaskDelay(1);
  }
}type or paste code here

[guix]

It makes no sense, because address and dataLen are of type uint8_t..

[Koepel]

At the bottom of this page: https://www.arduino.cc/reference/en/
You should know all of them.

[ak_duino]

Right. Im just not sure if Im calculating right.
If im
address>>8
modbusTCPClient would be
modbusTCPClient(10011100)
or
modbusTCPClient(156)???

[ak_duino]

Im just not sure if Im doing something wrong or if this is just some Tom foolery.
Im calculating

modbusTCPClient.write(156);
modbusTCPClient.write(64);
modbusTCPClient.write(0);
modbusTCPClient.write(5);
modbusTCPClient.write(10);

Im assuming these numbers are correct since the guy who wrote this is pretty talented coder.
That is unless my math is wrong.

[guix]

0x40000 is 0b‭1000000000000000000‬ in binary, that is 19 bits

address is of type uint8_t, so it can store only 8 bits (one byte), so it will keep only the first (right-most) 8 bits of 0x40000, so it will be 0

0 >> 8 = 0 and 0 & 0xFF = 0

This function is incorrect

I understand how you got 156 and 64, you are confusing 0x40000 with 40000, they are not the same! But 40000 is also too big for a byte

[ak_duino]

Alrighty.
well thanks for the quick response.
perhaps its 40000 in base 10 .That would be 16 bit or one word.
And perhaps this is just a "Shifty" way of taking the lower byte of a word
and doing some arithmetic.???

[guix]

Change the function to

void writeMulti( uint8_t id, uint16_t address, uint16_t *data, uint16_t dataLen )

Also change for ( byte i to for ( uint16_t i

Call it with writeMulti(2,40000,data,5)

It should give the expected result