BS2P-40 OEM - CPU not working?

Hi Parallax Team,

I have recently migrate my project from a integrated BS2P-24 to a BS2P-40 OEM microprocessor to allow for more pin as i also moved to a parallel LCD display and of course to reduce cost. I have prototype the new display using the 4 bit LCDCMD and LCDOUT commands and got the "Hello World!" test working fine so i'm not too worried about that part, but it seems when i moved the electronics onto a custom PCB - see attached PDF of the CPU schematic which closely mirrors the CPU schematic shared on Parallax webiste, ( CPU Schematic.pdf?dl=0), the processor seems to be dead. When i upload the code onto the board into the SEEPROM from the laptop it detects that a BS2P-40 is present and all of the files (multi-program) load successfully so i have to think that the code is present and loaded correctly.

There is +5V flowing onto the board and other parts of the board work properly.

As a simple test i defined Pins 0-6 as =1 (+5V) and used a multi meter to test the values and all of them seemed to be floating around 0.5 V. I am going to see if my reset logic (using a MAXIM 706 IC - ( connected to pin 7 is working, but after that, I'm not sure how else to tell if the CPU is working properly?

Any advice would be appreciated.



  • Mike GreenMike Green Posts: 22,928
    edited 2018-03-21 - 16:20:25
    If you can download code into the BS2p-40, the CPU and EEPROM are working properly. The CPU is actively involved in the downloading process.

    An I/O pin set to input mode (the power up default) looks like it's floating. If you set the I/O pins in your program to 1, this doesn't change the pin mode. You have to use an OUTPUT statement to change to output mode or you can just use a HIGH statement to set the mode and output state.

    Any time you have a puzzling situation or behavior, it's helpful to attach a copy of your actual schematic and the source code for your program, otherwise we're just guessing what's going on.
  • Tracy AllenTracy Allen Posts: 6,423
    edited 2018-03-21 - 21:22:23
    Super-simple programs indicadtors could help for Go-NoGo operation...
    --- a LED hooked to an output, simply flashing at 1Hz.
    --- a DEBUG"top",13 repeating at 1Hz while connected to serial terminal.

    In addition to the MAX706, check that the ATN pin is staying low after programming. If high, it holds the Stamp in reset.
  • Dear Tracy and Mike,
    I have tested everything out as you suggested and the processor is working perfectly. It is not resetting as far as i can tell - special jpeg for you guys :) I believe that the LCD panel may have been faulty.

    Thank-you both,
    3264 x 2448 - 2M
  • Check the PIN #s on Your development board against the PINs on your Stamp. They will change when using the extended I/O Stamps.
    I ran into this when moving from the BS2 to the BS2P40. The PINs are different on the board.
  • Also, if you're using the AUX pins, you must use an AUXIO command before any commands affect that pins.
  • Thanks also Antediluvian and Walt. I was careful to map the main pins and auxiliary pins. I seemed to get it to work....i believe the LCD panel got damaged somehow along the way, but after replacing it, it seemed to be fine.
Sign In or Register to comment.