client.Packager

[ailen1002]

st := modbus.NewSerialTransporter("COM3")
st.Mode = serial.Mode{BaudRate: 19200}
defer func() { _ = st.Close() }()
// slave1
c1 := modbus.NewClient(modbus.NewRtuPackager(1), st)
_, results1, err1 := c1.ReadHoldingRegisters(1, 10)

// change slave ID
c1.Packager.SlaveId = 2

// slave2
_, results2, err2 := c1.ReadHoldingRegisters(1, 10)

// change slave ID
c1.Packager.SlaveId = 3

// slave3
_, results3, err3 := c1.ReadHoldingRegisters(1, 10)

client.Packager Can modify SlaveId externally with uppercase first letter. Communicate with different slave stations

[hi-way]

change slave ID
c2 := modbus.NewClient(modbus.NewRtuPackager(2), st)

[ailen1002]

I have modified my usage code according to your method, and everything seems to be working well now, thank you