SERIN2 Receiving Wrong Data

[tumbleweed]

By lowering the baud rate you're now allowing device B (and SERIN2) twice the time to receive the bits and assemble the byte.
That's probably what's helping a lot more than any line noise issue.

A software UART has a lot of potential timing issues, especially when it comes to receiving.

[rsocor01]

By lowering the baud rate you're now allowing device B (and SERIN2) twice the time to receive the bits and assemble the byte.
That's probably what's helping a lot more than any line noise issue.

There is probably a little bit of both. I did a search in the forum, but couldn't find anyone having the same issue.

[Ioannis]

What is the clock of each PIC you use?

Ioannis

[rsocor01]

What is the clock of each PIC you use?

Ioannis

The sending device has the typical 18F4550 USB setup and it is set to "Define OSC 48". The receiving device is set to "DEFINE OSC 16".

[Ioannis]

I guess then, the sending device is interrupted by the USB routines while sending and as a consequence the transmission of RS-232 at that time is corrupted.

Ioannis

[tumbleweed]

If you're using interrupts on either end then you shouldn't use SEROUT/SERIN as interrupts will upset the timing.
You should use the hardware HSEROUT/HSERIN routines, but then you will have to use the dedicated UART IO pins.

Also, you would be better off running the receiving end with a faster osc setting... try 32MHz instead of 16.

[richard]

I guess then, the sending device is interrupted by the USB routines while sending and as a consequence the transmission of RS-232 at that time is corrupted.

that can't be right because

I know device A is sending the right data because I can see it with a logical analyzer.

my next guess is that device A is running on 3Volts
this guessing game has got longer legs than i expected

[rsocor01]

If you're using interrupts on either end then you shouldn't use SEROUT/SERIN as interrupts will upset the timing.
You should use the hardware HSEROUT/HSERIN routines, but then you will have to use the dedicated UART IO pins.

Also, you would be better off running the receiving end with a faster osc setting... try 32MHz instead of 16.

The PIC ports with HSEROUT and HSERIN are already taken. Using a baud rate of 9600 instead of 19200 made a difference. It is now working fine. The USB Darrel's interrupt takes micro seconds to execute. I measured it once. I forgot the exact number, but it was very small. That shouldn't affect the SEROUT/SERIN.