Start the IAR Embedded Workbench.

Ensure that the cable  is plugged in the parallel port.

Choose "Create New Project in Current Workspace"

Choose ASM only project

Choose where you want the project to be on your disk.

This will create  a simple project that has a sample asm file in it.

Copy the ats3b_digi-33.s43 file into the project directory/folder.

When you have the workspace look in the left panel and "right click" on the workspace name, Click on "Options".

Choose General category.
In the "Target" tab ensure the correct device is selected "msp430f1121a"
Click on the box to choose "Assembler only Project"

Choose Linker category.
Processing Tab: ensure that the "Fill unused code memory" box is checked.
Should be filled with 0xFF.

Choose Debugger category, Make the driver "FET debugger"

Choose FET debugger category, click the box "Verify download"
Ensure that the connection is the correct port (LPT1)

Right click on the project in the left panel and "add files"
Click on the filter to see assembler files (*.s43) and choose the firmware file.

Click the X in the right panel to delete the edit for asm.s43 (the example file)

Right click on the asm.s43 filename in the left panel and remove it.

Double click on the file for the firmware you just added to open it in the edit window

Press F7 to compile it - check there are no errors.

Power up the ATS3B, and connect the programming cable.

Press Ctrl-D to start Debug, this is what does the actual download.
You should see dialog boxes showing the chip being erased, programmed and verified.

In the Debug toolbar that appears, click "Run", then click "Exit Debug"

Power down the ATS3B and disconnect the cable.

Test it!