Jan, you are such a kidder, trying to ruffle Erik's feathers like that so that he will give us another one of his famous sermons. Well, I will save him the trouble so that he can sit under a tree with a nice cool lemonade and enjoy his weekend:


(You're welcome, Erik. :-))

Now, here are the bugs I found in the code for the quiz:

One

   sjmp  ISR_UART_Echo    ;  and leave, echoing back the CR

At this point, the accumulator has been clobbered and the code at ISR_UART_Echo will transmit the message length byte, not a CR. I don't see how this this could have worked in the simulator.

Two

    cjne  r0,#RxBuff+RxSize,ISR_UART_Store

This is a classic "off by one" error that allows the buffer to be overrun by one byte. It doesn't show up in testing because the byte immediately following the RxBuffer isn't being used. Maybe Jan didn't even see this one?

Three

Since the program is using R0 in register bank 1, the stack pointer must be initialized to address 8 or higher so that there is no conflict between the stack and R0 in bank 1.

Four

The program doesn't initialize R0 in bank 1, so for the first input line, the program will store characters at some undetermined memory location, not in RxBuf as expected.

At least that's how it looks on the surface. But wait, he TRIED!!! it and it WORKED!!! Could it be that Jan has played some diabolical trick on us? Perhaps with the line

   lcall RxString

Hmm. I wonder ...

-- Russ