Which Modbus function code is used to read multiple holding registers from a device?
Holding registers are typically read with a function code starting with 0x0.
Function code 0x03 is used to read holding registers in Modbus protocol.
Given a Modbus TCP request packet to read 4 coils starting at address 0, what is the expected byte count in the response?
Each coil is represented by 1 bit; 8 bits make 1 byte.
4 coils require 4 bits, which fit into 1 byte of data. The byte count field in the response PDU is 1.
Which serial port configuration is correct for a Modbus RTU device operating at 19200 baud, 8 data bits, even parity, and 1 stop bit?
Parity 'E' means even parity; 'N' means no parity.
The correct configuration is 19200 baud, 8 data bits, even parity (E), and 1 stop bit (1), which is '19200 8E1'.
A SCADA system using Modbus TCP cannot read data from a slave device. The network is confirmed working. Which issue is most likely causing the failure?
Modbus TCP still requires correct slave addressing.
Modbus TCP uses unit identifiers (slave IDs) to address devices. An incorrect slave ID causes no response despite network connectivity.
Arrange the correct sequence of steps a SCADA master should follow to poll multiple Modbus RTU slave devices on a serial line.
Polling requires sending request, waiting for response, processing data, then moving to next device.
The correct order is to send the request, wait for the response or timeout, process the data, then repeat for the next slave device.