Monday, January 03, 2011

Update on ‘broken’ output ports and other trivia

P0.2/P0.3 (port not going high) -- 10K pull up on each port fixed problem.

P1.22 (port ok, row transistor not going high) -- solder short on output resistor on controller board. No danger to any device, short removed.

P1.28 (port being low) -- This was a bit of solder between the actual microprocessor IC pins for P1.28 and VSS_A. Moved with a scalpel. (Most likely during construction of controller board rather than a manufacturing fault on the microprocessor board).

P0.23 -- The ‘flickering’ on logic high seems to occur when my hand or the whole board is near the computer. This doesn’t happen on other ports. Logic low doesn’t seem to do this. When in circuit it seems ok (although slightly noisy under same circumstances) - so I’m going to leave it for now and see if it causes a problem on that row. The port voltage itself seems ok, and the transistor for that row isn’t turning on.

For interest, here are the port assignments used for the display.

Function -- Position -- Port

Row Select Number (Inverted) -- bit 0 (LSB) -- P0.2
Row Select Number (Inverted) -- bit 1 -- P0.3
Row Select Number (Inverted) -- bit 2 -- P0.4
Row Select Number (Inverted) -- bit 3 -- P0.5
Row Select Number (Inverted) -- bit 4 (MSB) --P0.6

Column Enable (1=on) -- 7 to 23(MSB, left-most of graphic) -- P1.16 to P1.31
Column Enable (1=on) -- 2 to 6 -- P0.25 to P0.30
Column Enable (1=on) -- 0 (LSB, right-most of graphic) to 1 -- P0.22 to P23

  • Row Select Number 0 = top row
  • Row Select Number 19 = bottom row

The split of column enabled into three ranges is mainly due to the available ports on the microprocessor board, but this are not a problem since we operate basically in the range of milliseconds, and code to split up the graphic is trivial. (I’ll share this in a future post.)

A Note on terminology:

I use the term microprocessor and microprocessor board rather than microcontroller and microcontroller board in order to clearly separate it from the LED display ‘controller board’ in this blog post and the previous one.


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