Matrix Orbital Corp

Hi,

I'm using a GLK12232-25-SM in an application where a large number of LCD displays are written to regularly over a long duration. At the default baud rate of 19200, bits are occasionally flipped during transmission. With no error-detection on the comms protocol, weird things occasionally happen. For instance, sometimes the font metrics get set to something random such that the text does not display legibly. This means that at any given time, at least one LCD is often playing up -- an undesirable situation to say the least.

Why is there no error checking? And is there anything we can do to avoid these problems? We could write all the settings (contrast, backlight on, font metrics, etc) to each unit on a regular basis, but I wonder if too many writes will be bad for the unit's memory (and it sounds like a hack). Unfortunately the unit doesn't allow for querying of the state, so we can't check to see if it's changed before writing. Is there a better solution?


Thanks,

Alex

What usually happens instead of bits being flipped is that the internal incoming data buffer is overflown. If you are having problems its probably the best thing to verify that you are using flow control as described in the manual.

Hello Ray,

Thanks for the reply. I don't suspect flow control to be the problem, because the data rate is very low: text only, written at 0.5Hz. Is buffer overflow really feasible?

Hi Alex,

I see you've got a few questions left here, so I'll try to get those cleared up for you.

There is no error checking, we thought this would tax the communication system too much for the small benefit it may provide. Serial protocol is usually rather stable. There is flow control that can be used to determine when the buffer is almost full, with almost being a user defined value.

Setting changes are rare, but I understand you've got a number of units all running simultaneously, so any errors are magnified. It is possible to put a software lock on the settings, you can check out set and save data lock in the manual. As you've seen, it is possible to inadvertently send a command to change settings, this makes is much harder to do so. You can even lock down everything but transmission to the display.

For writing to memory, the EEPROM is rated at 100,000 writes, so it's recommended that the settings be saved once and left. Merely setting the settings, without saving, won't write to memory and can be done on start up or intermittently if need be.

If you have any further questions regarding you display or the communication protocol and locks associated with it, please don't hesitate to post.

Thanks,
~Troy

Thanks very much Troy, I'll have a look into the software locking when I next get a chance.


Alex