Usart: Stop bits = 1, 1.5, 2...?

[Laurent Chouinard]

So i've searched the Microchip datasheets, the CCS documentation and this forum. So far I am pretty sure about the answer but I'd like the verify here first just in case I missed something.

Is there a way to adjust the length of the stop bit of the hardware USART of a PIC16F7x?

Before you answer: Yes i know about the 9th bit, but I already use it
Still before you answer: No i can't make my own software-based serial port, I need the CPU time and interrupts running.

I basically need a 1.5 stop bit on a 9 bits data communication. I think i'm screwed.

[asmallri]

Just confirming what you already know - you can't do it with the hardware UART. Its still possible to do it with your own software UART. I have a 18F452 PIC running at 40MHz that has two software UARTs running full duplex at 115Kbps plus a HW UART and a full speed USB interface.

For the software UARTs it requires a timer (preferably two) and an interrupt pin per software RX pin (for start bit detection). In my cast the interrupt handler was coded in ASM but I have test a single SW UART at 115Kbps using the same technique with CCS C.

Disclaimer - it is far easier to do this with an 18F series pic than a 16F series pic because of the hardware interrupt priority support
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Regards, Andrew

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[Ttelmah]

There is a sort of 'trick'.
For receive, you don't need to do anything. Unit set to 1 stop bit, will happily receive data with 1.5 stop bits. For transmit, use the option to control a 'data available' line ('enable=pin' in the use_rs232 setup), and connect this pin 'back' to an interrupt input on the pic. In this interrupt, trigger a hardware CTC timer lasting for half a bit time. When this interrupts, send the next character. You can do the same in software, by checking the transmit shift register empty bit, then waiting for half a bit time, but the hardware interconnection, allows other things to be done while waiting.
It is not easy, but can work.

Best Wishes