Displaying Jibberish

hyrdra · Post by **hyrdra** » Fri Dec 12, 2003 8:25 pm

Hi,

I recently purchased a LK204-25-WB from Parallax.com, for use in an upcoming project with a Basic STAMP microcontroller. I wanted to test the LCD real quick and perhaps design a user interface in Windows, so I connected it up as the manual says (note that Matrix didn't have an exact manual for this model, so I defaulted to LK204-25).

Everything with the LCD seems to be fine, however, when displaying any type of text, even from a basic terminal program the thing displays nothing but jibberish, that is, not conforming to the standard character set or even it's own default font-map.

On Parallax's web site, they say this version is pre-modified for usage with TTL level RS-232 voltages, so it's a drop-in solution for their microcontroller. Could this be the cause of the problem or do I have a defective display? The power-on splash screen displays correctly but everything after that is completly incoherent. Port settings are correct.

I haven't yet tried to use it with my Basic Stamp, but I don't want to go to all that trouble if there is in fact a problem with the display.

Any help or insight is greatly appreciated.

Thanks!

hyrdra · Post by **hyrdra** » Sat Dec 13, 2003 2:51 am

Hi,

Just a side note, I tried virtually all combinations of port speed settings, etc. with no luck. I didn't try the "manual over-ride" or memory reset because this wasn't mentioned in the LK204-25 PDF file, and I don't know if its supported or not.

Thanks for any help ahead of time.

Post by **Henry** » Sat Dec 13, 2003 2:54 am

All the units sold by parallax are in TTL format.

hyrdra · Post by **hyrdra** » Sun Dec 14, 2003 12:49 am

Yeah, but is this the cause of the problem of incorrect/garbled display...the voltage difference?

Miles · Post by **Miles** » Tue Dec 16, 2003 11:10 am

How are you trying to communicate with the display? Are you using a Basic Stamp or are you using a PC?

hyrdra · Post by **hyrdra** » Tue Dec 16, 2003 9:00 pm

I am using a PC via the standard RS-232 9-pin serial interface on the back of the module, directly connected.

If this is in fact the case, would it be possible to use a voltage-limiting resistor on either serial input/output to use a PC to communicate with the display? I would really like to design my text-interface using a PC.

Thanks for your help.

Miles · Post by **Miles** » Wed Dec 17, 2003 12:34 pm

Unfortunately there is no easy solution to convert the TTL levels. Modifications have been made to the PCB to ensure TTL levels were achieved. We use a RS232 line driver which accepts the 232 levels but the microcontroller needs TTL CMOS levels to communicate. This is why the line driver is used. All basic stamps have TTL communication, therefore we modify the units at that level. Not all Basic Stamps have the ability to ouput RS232 levels.