you say, "It most certainly does: it is always there." to which I'd respond that I've never seen it in an 8052. It may be in some parts, but not all of them.

The resident debugger is the same on any component that is physically 805x compatible. With others, including your SilLabs parts, one has JTAG when it IS supported, just as is the case when I use 805x IP in an FPGA. Which pins do you have to give up in order to use JTAG on your 40-pin DIP or 44-pin PLCC parts? I'd be interested in knowing what JTAG-compatible parts I could potentially use today. Unfortunately, I didn't work them into the products I designed back in '85 or so.

RE