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'[PIC] Problems (?) with Digital/Analog I/O in 18F'
I am posting this here because I can't get to the Microchip website (to read data sheets) - it appears to have been down for at least the last 3-4 hours (since about 11AM eastern time).
Reading (here) that my beloved 18F452 was going obsolete, I got the latest software upgrade for MPLAB and my EPIC programmer, and ordered some samples of the three parts (above). I got the samples, took one of my standard test programs, and reassembled it for each of the 18F4520, 4525 & 4620.
I programmed the test code into each chip and proceeded to test them. All three APPEARed to work - lights blinked and they responded to RS-232 commands by returning apparently correct information.
I say apparently - the IP_Relay device has some digital outputs (Port B) and analog inputs (0...4) - for testing the digital outputs are jumpered to the analog inputs. The test code toggles all of the output bits ON and OFF, and reads the bit state both digitally and via the analog inputs. The test should indicate it is turning the outputs ON, the display should show them turning ON and the voltages should show +5.0? volts. Turn outputs OFF, display should show them turning OFF and voltages should show near 0.00 volts.
Doesn't happen - ON or OFF command has no effect. Digitally outputs show as always OFF and voltages are always reading +3.959 volts - exactly the same on all 5 analog inputs. Nothing is getting hot, so nothing appears to be fighting in some stuck state. The indicated voltage is actually different from chip to chip, but always the same on any given chip.
I know there is an option on these chips to default PortB to analog or digital at power UP - I tried that setting both ways with no change. Anyway, I would assume the code would override whatever the default power-up state is. I did look at these data sheets on-line when I ordered the samples, and didn't see any obvious changes which would interfere with the port operation.
So does anyone have a clue as to what changed that would make the ports and A/D operate differently? I am guessing there is something I need to enable or disable, but Microchip's website is still down. So at the risk of annoying someone here I'll ask if there is an obvious gotcha! that I should know about.
Roy J. Gromlich - Senior Engineer
5000 Ritter Road 2nd Floor
Mechanicsburg, PA 17055
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