RS-232 works fine at 9600 and it fails at 19200

[MAC_08]

Hello and thank you in advance for your help.

I'm using a 16F818 @ 4MHz to transmit some bytes to a PC. I'm using the instruction #use rs232(baud=9600, xmit=PIN_B2, rcv=PIN_B3) and I'm receiving all the bytes correctly in the PC. However, if I change the speed to 19200 I get some errors and some bytes are not transmitted. The line driver is a MAX232 with four 1uF capacitors.

The only interrupt is the Timer2 which is activated every 20ms to increase a counter.

Do you know what can be the problem?

[Guest]

Hi,

Standard questions:

1. Compiler version??
2. Which PIC are you using??
3. What are your fuses??
4. Crystal, resonator, other??
5. Do you have a SMALL, complete program that demonstrates the problem??

Jeff

[PCM programmer]

The 16F818 does not have a hardware UART, so you are using a software
UART. If a software UART is interrupted during transmission or reception,
the bit timing will be disrupted. This is likely to be the cause of your
problem. To prevent this, add the parameter shown in bold below.

[asmboy]

This is HONESTLY not a snarky comment.

I learned fast about when the software UART is OK

If I don't care about RS-232 RECEIVE functions ( just gonna be a TALKER)
- I will use ANY pic and the software UART is fine. At pretty much any baud so long as INTS are OFF when sending.

BUT

If I need to RECEIVE characters - I just choose a pic with a HARDWARE USART.

At other than low bauds you are at risk of exactly what has happened.

[Marc]

Thank you all for the replies.

Here is more information:

PIC16F818 @ 4MHz
CCS Compiler 3.187 (IDE 3.42)
FUSES: XT WDT PROTECT PUT NOBROWNOUT MCLR NOLVP CPD NOWRT NODEBUG

The PIC only sends some bytes (7 or 5) depending on the key you press on the keyboard. The bytes are sent as simple bytes (%c) and not as Integers (%d) or strings...

Code Example:

[Marc]

I think that I have solved the issue!! Thanks PCM Programmer!!

This is what I have modified: