LCD problems using SEROUT 16

hvguy

I have the Parallax 4x20 LCD, item 27979, connected to a BS2 and have had no problems with it until I tried to use the Sout pin.

This code:

DO
PAUSE 100
SEROUT 0, 32, [noparse][[/noparse]"hello"]
PAUSE 1000
LOOP

Displays hello every 1.1sec, as you would expect, with the LCD connected to P0

This code:

DO
PAUSE 100
SEROUT 16, 32, [noparse][[/noparse]"hello"]
PAUSE 1000
LOOP

Displays a cursor at L0 P0 and does nothing else, with the LCD connected to Sout

What's going on? Why does Sout not work the same as P0?

allanlane5

Because Sout expects to have a PC connect to Sin -- the BS2 modulates the Sin signal to make the Sout signal. Also, Sout usually is +-5 volts or so, where pins zero through 15 are all TTL -- 0 to 5 volts.

hvguy

Thanks for the input. I checked Sout on the scope and found it's output to be the right level, 0-5V, however it was inverted. I checked the manual to see if this could be fixed with code and found: "If Tpin=16 is used, the data is inverted and driven regardless of baudmode setting". Given this statement I simply inverted the output with a 2N7000 and resistor, and now it works fine.

Post Edited (hvguy) : 5/7/2010 4:55:21 AM GMT

allanlane5

Wow, you're good. Yes, I was going to mention the "inversion despite the baudmode setting" thing.

hvguy

I'm new to this uC thing, but I have a lot of experience designing analog and digital electronics, I just needed someone (you) to point me in the right direction. Thanks!

Chris Savage

I'm not sure where it went, but we have published the schematic for driving the LCD from the programming port using an NPN transistor to invert the signal. Takes a transistor and 2 resistors. A 2N3904 would work as well.

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Chris Savage

Parallax Engineering
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