Modbus RTU

Instead of a second PC and a null modem cable, you can also use virtual null modem software $($vnullmod$20-$ downloadable from the Internet or Eltima or TAL software$)$ and run both RTU master and slave on one machine. Just do not use a COM port that already exists on your machine $($such as COM$1).$ This can also be run in the Remote Labs.

IMPORTANT: Change the slave ID to $4$ and set coils $12/13($absolute addressing in decimal$)$ so that your data $($bit values$)$ with a $$read coil$$ command $($FC$01)$ becomes $03$ hex $($i$.$e$.00000011)$ in the response message.

IMPORTANT: Address ONLY these two coils.

a$)$ Provide screenshots of BOTH the Modbus Poll and Modbus Slave screens showing the requests and responses. $($Display$$Communication$).$ Capture a minimum of four Modbus transactions: one with both coils cleared, one with both coils set, and one each with one of the coils set.

b$)$ Explain why you have chosen the two specific coils you are reading. This, in turn, will show that you understand the difference between relative and absolute addressing.

c$)$ The correct data returned, with both coils set, will be $03(00000011).$ Which $1$ belongs to which coil?