UART Output is limiting to 20 Characters

[jay_dee]

Hi,
I would appreciated a second opinion on this.
Attached is a simple bit of FC used for testing another program. It builds a string and sends this out over the UART at 57Kbit.
A assembled string can be over 20 characters
FC is attached.

In simulation the output stream is fine, both UART Console and the assembled string shown on a console Writer are fine, with strings over 20 Characters

Serial_Diag_Console.JPG (47.51 KiB) Viewed 593 times

hardware is PIC18F2585 and the output string is always tuncated to 20 charaters. I dont think it is a hardware limitation.

~1,9,1,MyValue ECT,2$
~1,10,1,MyValue ECT,$
~1,11,1,MyValue ECT,$

I'm fairly sure the error is somewhere in the string concatenation, as the last value (my terminating character $) is always correctly added.
But the value (just before the terminating character) is being truncated to a length that always results in of 20 char max.

I've checked my FC variable to ensure everything is sized to handle a string larger than this, but the problem persists.
Any Thoughts? J.

[stefan.erni]

Hi jay_dee

one question:
Do the 4 strings have to add up to 30 instead of 20?

2025-08-18_14-42-01.PNG (15.45 KiB) Viewed 576 times

[jay_dee]

Thanks,
My string contents will have a varying length.
It does not appear to make any difference what length I make the resultant's String length. i.e. TXstring[25]
I dont know the details of how strings are concatenated TBH, But I presumed that if an actaul string was 4 characters but the string containing variable was declared as 10 characters, that is just a limit on the size reserved in memory.

I have tried various sized strings for the resultant, including 30...no improvment.
Hmm. J.

[stefan.erni]

Hi jay_dee

Sorry, my help was wrong. I didn't notice a line.
I think you're doing everything right. Maybe you can split it into two strings as a test.

PIC18F_SendDiagnostic_V4_WIP.fcfx

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2025-08-18_15-28-35.PNG (218.02 KiB) Viewed 566 times

[chipfryer27]

Hi

I'm not sure if this is still the case, but previously FC had an issue in concatenating strings if you tried to do multiple concatentations at once

Test$ = ""
Test$ = Test$ + "abc"
Test$ = Test$ + "123"

Would give you Test$ = "abc123"

However if you tried

Test$ = ""
Test$ = Test$ + "abc" + "123"

Would not give you the expected result.

May not be the issue anymore though.

Regards

[jay_dee]

Thanks Guys,
I forced the "UART Send String" macro to send -- .TxString = "~1,1,1,My Value ECTBB,12345$" which is more than 20 Char
This is sent fine, so its not a hardware or UART buffer issue.

Looks like a concatenation issue with strings over 20 char.
I cant find a working concatentaion method yet, So I'll be interested if the FC team know of a good workaround or known issue.

In the mean time, I'm splitting the String into Two, and just sending them one, after the other. Bit clunky but seems to work.
Thanks, J.

[chipfryer27]

Hi

I frequently send strings many tens of characters long (usually somewhere between 80 - 120) out over the UART. However I always create my string in small chunks as mentioned above, adding one string at a time.

Regards