In SX Microcontrollers, SX/B Compiler and SX-Key Tool, tdg8934 wrote:

Here is the latest summary:

I have a program written for a Parallax Basic Stamp 2 (BS2) microcontroller and 8255 Interface circuit that works with 4.9v on CS and WR control lines and ~0v on A1, A0 and RESET control lines.

I wrote a almost 1-1 identical program for Parallax SX-28 microcontroller. However, as originally written, I get 2.2v on CS and 3v on WR control lines and ~0v on A1, A0 and RESET control lines. I can even pull all of these control line wires between the SX-28 to the 8255 and take measurements directly from the SX-28 and get those same 2.2v and 3v measurements. 

I tried adding a 74HC245 buffer (/OE tied to ground and DIR tied to +5v) on CS and WR control lines between the SX-28 and 8255 and saw no differences in the voltages readings (2.2v and 3v). I removed it.

I tried adding some pull up 10K resistors from +5v to the CS and WR lines and saw no changes in voltage (actually a bit of a drop) and no circuit working still for the SX-28 and 8255. I also tried resistors from ground to the CS and WR lines and it did not work either. I removed the resistors.

What is different between the BS2 and SX-28 to cause different voltage differences of 2.2v and 3v when the BS2 generates 4.9v on both control lines?

I have run out of ideas on this one. Please help (anyone).

Thanks.

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