While your comment is certainly valid, I'd take exception with the notion that the MCU shouldn't execute his code if it's assembled for execution at 0x000. So long as he's absolutely certain he's not initialized the MCU, which it appears he hasn't, no interrupts should occur, so his lack of reset or interrupt "vectors" should be just fine, though it would not be acceptable for release.

One other thing ... Does the 805x actually have "vectors" as some microprocessor/microcontrollers have? I thought they simply provide locations for jump instructions. The old 6502, by contrast had vector space, in that all that was needed to direct a reset or an interrupt was a target address, and not a complete instruction. I'm persuaded that that's the difference between an instruction and a vector. Am I wrong here?

Oh, and BTW, I ran that program through the simple simulator the MIDE51 provides, and it seems to simulate properly. Clearly, if the program was assembled to execute at 0x000, it should do something other than what has been claimed, i.e. all the port pins remain high. I'd guess that (a) observations haven't been made with the correct instrument (an oscilloscope), or (b) something is amiss with the way in which the MCU was programmed, or (c) the program wasn't assembled to run at 0x000.

RE