BasicStamp and 633

[chrisdlove]

Good evening CF Tech,
I have replaced the LCD display with a new one and tested everything on the CPU and ensured all signal were correct Vo=1.0 V DC, all other signals were triple checked. After powering up, the LCD display worked perfectly!



Thank-you very much for the advice and help!
Regards,
Chris.

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[CF Tech]

Hey! That looks fantastic. Good work

 

[chrisdlove]

Hello CF Tech,
in further work with the display, we have encountered some noise which has caused the display to become corrupt - it still seems "alive", but the display shows garbled characters, i.e. backwards question marks, etc. Power cycling the LCD display restores everything correctly. We are working to improve the power quality, however this brings up a good opportunity to pulse the LCD display periodically and reset it proactively if something like this happens in the future. One suspicion is that because we are using the parallax BS2P48, 4 bit mode, DB0-DB4 pins are unused. Parallax suggested to provide pull-down resistors as shown in attached jpeg. As well, there is an additional 10K resistor connected to Enable (E) pin. I have added this extra electronics to my board now, but the LCD corruption has still been seen at least in one instance suggesting this is not the source.

If the Hitachi display is still alive, but the output is garbage, what would cause such corruption and how could i detect it proactively and correct it? If you have some advice or other ideas , they would be welcome.

I will share my results with the forum members if i also get this working.

thank-you,
Chris.

 

[cosmicvoid]

... If the Hitachi display is still alive, but the output is garbage, what would cause such corruption and how could i detect it proactively and correct it?

My $.02...
It would be difficult to determine whether the display is "still alive" (i.e. can receive and execute commands) remotely. The only clue is seeing the garbage. Possibly, this could be due to a power transient; perhaps a 10uF 16V capacitor right at the display power/gnd pins would help.

Since a small text display does not show a lot of data, one proactive strategy could be to give a "clear all" command, and resend the desired text from a memory buffer for every update. This presumes the LCD controller is still responsive. No way to determine that other than visually, I think.

Pulsing the LCD power off/on before resetting would cure all ills, but you're liable to get transient junk on the screen before the "clear" command can erase it.
end of $.02

 

[chrisdlove]

Thanks for the $0.02 cosmicvoid I was thinking to add some decoupling caps to ensure i'm not getting any voltage spikes which may disrupt the Hitachi controller. I have a keypad and can see the characters changing on the display - although its hard to tell if any are correct...its kind of like the display memory map has been corrupted and the desired characters have been remapped randomly....clearly some form of corruption.