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Some questions about CFA634 character addressing


New member
Hi there!

I am new to the forum, but I have made use of the search function Before posting this ;)

I am going to get one of these displays, and I need to know a few things beforehand.
I am confused about a few things in the PDF sheet for the CFA634 series, and I hope I can get some answers to my questions...

Horizontal bar graph:
It says that it is going to use some of the custom characters. Does that mean that the characters 128-135 are populated by elements for that if I have not replaced it with my own characters? Then what are the characters 208-212 and 214-222 for?

Big character mode:
There is something mentioned in the PDF about large character mode. I guess the display itself doesn't have a mode like that, and that you need to make your own from custom elements? But if I send custom characters to position 128-135, will the bar graph be inoperable?

I really like these products :)
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CF Support

Welcome to the forums!

Glad to hear that you enjoy our modules, hopefully I can clearly answer your questions.

Both questions involve the special characters set. There are 8 custom characters on the CGRAM \000-\007.

Because there is only one customer characters set, all command must share. This includes the above two commands as well as Set Custom Character Bitmap (\025, 0x19). Because we want to make sure that the Horizontal Bar Graph and Big Characters are always printed correctly, the firmware will replace the contents of whichever special character set it needs to use.

That is why we recommend you don't use both of them together without some special care as you will "step on" the contents of the bar graph while using the big characters, for example.

characters 208-212 and 214-222 are not full height characters and therefore weren't deemed "correct" for what we want to use the horizontal bar graph for.

Hopefully that answers your questions.

If you have any more questions, please feel free to reply on this thread or send an email to support@crystalfontz.com and we'll get you taken care of.


New member
Yes, thank you for the answers. It is a little bit clearer now.

And if I have not got it wrong, these displays don't have a special (native) command for going in to a "large character mode"? The reason I ask about that is because large characters are mentioned sometimes in the documentation, and I don't understand why unless the display had a special mode for it.

My setup will include one or two CFA634-YFH-KL displays.

The picture upload function doesn't seem to work, otherwise I would have shown you an approximation of what it would look like.
USB LCD Displays - Graphic and Character LCDs with a Keypad

CF Support


You are correct, neither the older version nor the new version support a large character mode. Because we liked the idea, we wrote up the functionality.


New member
Thanks! :D

I do have another question as well:

In the initial startup phase, is it ok to send a lot of consecutive bytes with config information? (After it has booted and settled)

Like this:

SEROUT Display, T19K2, [004, 009, 000, 000, 009, 001, 001, 009, 002, 004, 009, 003, 004, 009, 005]
(Hide cursor, permanent display output, user display, logic level serial, 115200 bps, save settings)

And is that format also valid for everything else I want to send to the display? Nothing else that needs a pause?

Also, when does the baud rate speed change occur? Directly after the command?

Should I do something like this instead:

SEROUT Display, T19K2, [004, 009, 000, 000, 009, 001, 001, 009, 002, 004, 009, 003, 004]
SEROUT Display, T115K2, [009, 005]

CF Support


With the exception of the commands that write to the EEPROM, the buffer should handle the burst of text no problem.

It might take a little trial and error to figure out the best combination for your situation but it certainly is doable.

In regards to the baud change, it takes effect as soon as the command is issued so you would do as you showed in the second example above.
With one exception, each of the interface and baud rate changes all internally issue the save command (009, 005) so saying 009, 003, 004 does the baud change and a save.