To start a new program in a Siemens S7-1200 PLC, you'll need Siemens TIA Portal (Totally Integrated Automation Portal) software installed on your computer. Follow these steps to create a new project and program for the S7-1200 PLC:

1. Launch TIA Portal:

   • Open the Siemens TIA Portal software on your computer.

2. Create a New Project:

   • Click on "Create new project" or select "File" > "New" > "Project" from the menu bar.
   • Specify the name and location for your new project.

3. Select PLC Type:

   • In the "New Project" dialog, select the PLC type. Choose "S7-1200" from the list of available PLC types.

4. Add Hardware:

   • In the "Devices & networks" view, right-click on "PLC" and select "Add new device."
   • Choose "S7-1200" as the device type and specify the CPU model (e.g., 1212C, 1214C, etc.).
   • Connect your S7-1200 PLC to your computer via Ethernet or USB, and then click "Continue."

5. Configure Hardware:

   • Follow the prompts to configure the hardware settings for your PLC, such as IP address, subnet mask, and PLC name.

6. Create New Program:

   • In the "Device view," expand the PLC device tree and double-click on "Programs."
   • Right-click on "Program blocks" and select "Add new block" > "Program."
   • Choose the programming language for your new program (e.g., Ladder, Function Block Diagram, Structured Text) and specify a name for the program.

7. Write Program Logic:

   • Double-click on the newly created program block to open the programming editor.
   • Write your program logic using the selected programming language. You can use standard PLC programming instructions and functions to create your program.

8. Compile Program:

   • Once you have written your program logic, click on the "Compile" button to check for any syntax errors or warnings in your program.
   • Address any errors or warnings that appear in the compilation results window.

9. Download Program to PLC:

   • Connect your S7-1200 PLC to your computer via Ethernet or USB.
   • Make sure the PLC is in STOP mode.
   • In the "Devices & networks" view, right-click on your PLC device and select "Download to device."
   • Follow the prompts to download your program to the PLC.

10. Put PLC in RUN Mode:

    • Once the download is complete, switch the PLC to RUN mode to start executing your program. You can do this by toggling the mode switch on the front panel of the PLC.

Congratulations! You have successfully started a new program in a Siemens S7-1200 PLC using TIA Portal. You can now continue to develop and debug your program as needed.