Hi Daniel, and Thanks.

That post didn't apply, but the thread did. Thanks.

For the record, and just in case someone references this thread in the future, I will summarize my resolution.

First, there are two registers that are associated with the Address 0x99, called SBUF. One is an input register and the other is an output register. In the final analysis, the hardware determines which register to use based on the opcode being executed.

Now just in case that isn't confusing enough, there are two "windows" in Keil µVision debugger that relate to the serial port. One is correctly called a dialog box, and the other is an actual window.

The dialog box is labeled Serial Channel. It displays boxes containing the contents of SCON, SADDR, SADEN, some showing the states of bits like TI and RI, basically all of the things pertaining to the Serial Port. One of these boxes is labeled SBUF, but it only reflects the contents of the SBUF output register. The software will allow you to enter new values into this box, but it does not actually simulate input.

The second window associated with the serial port is an actual window, just like the one displaying your source code. This window is labeled Serial #x (usually Serial #1).

To display Serial Channel (the dailog box), pull down the "Peripherals" menu and select "Serial." To display the actual window, Serial #x, pull down the "Window" menu and select it from the list.

The simplest way to simulate input is to type it into the window Serial #x. However, pay note that unless your code echos the input data back to the serial port, you won't be able to tell that you typed anything by looking at the window. Instead, you'll need to look at the various registers and ports being displayed.

There are other ways to simulate input to the serial port, and they can be found at the link posted by Daniel.

Now that this problem is solved, I can get back to trying to figure out what's wrong with my project.

Thanks everybody.

Joe