Serial Flow control (RTS/CTS handshaking)?

Mar 23, 2006 at 2:05am

Serial Flow control (RTS/CTS handshaking)?

So, I’m making a nice little abstraction for the PIC 8 hobby servo controller at
I’ve got it built and more or less working, nice abstraction with GUI etc…

But it’s kinda flaky/jumpy. I’ve e-mailed the person who designed the HW, and he suspects that I’m writing serial data when the PIC is doing other things, and it’s misinterpreting my commands.

This makes me sad.

Is there any way to make the serial object obey hardware handshake flow control? I’ve looked through other people’s posts, and I’ve not found one that uses it.

I believe the USB serial adapter I’m using supports said flow control, though I can also test on a PC with built in serial (I’m using Mac OS X 10.4)

Thoughts? Assistance? Flying pigs?

I wanna get this working so I can release it and people can build cooler stuff easier.

Thanks! I’ve been banging my head against this for a few weeks now.

Mar 26, 2006 at 11:20am

Try sending one or both of the following to the serial object:

“dtr 1″
“xonxoff 1″

And let me know if it helps. There are many, many configuration options
available for serial ports/devices and we have added support for
additional ones as necessary. RTS/CTS is, at this time, not directly


Mar 27, 2006 at 1:18am

Unfortunately, if I can’t do at least CTS then it’s gonna require a full software/hardware redesign :/

The PIC chip is doing PWM for the servo control, and it’s just not fast enough to receive serial data at the same time, so CTS is being used to signal when it’s clear for the computer to send commands.

DTR goes the wrong direction, unfortunately-the PIC chip can’t listen and PWM at the same time

You say rts/cts isn’t “directly supported”…What’s that mean, is there some workaround?

I have a feeling it’s going to be very useful for me to have this support. I’ve been hoping for a while to make some free/open hardware interfaces that can be used with Max for controlling LEDs and relays and stuff like that.

Let me know if there’s anything that can be done, or an external or something I could use.


Mar 27, 2006 at 8:49am

Sorry, it was unconscious double-speak to mitigate my guilt that it’s
actually not at all supported. I can look into what’s involved with such
support for a future release of the object. Such a release will likely
not be in the super-short-term, so you might want to look at alternate
solutions. Possibly there is something you can do in the mxj object,
although I am not certain of that.


Am 27.03.2006 um 3:18 Uhr schrieb Sean Stevens:
> directly supported

Mar 27, 2006 at 8:15pm

I had a feeling that’s what you meant :P

I guess I’ve gotten spoiled by the wonderfullness that is Max/MSP/Jitter, and expected everything to just work/be easy.

Well, I guess I’ll hope that the Gods of Max smile upon me at some point in the not too distant future.

And, uh, I guess I’ll try and redesign with something using a UART for now.

Thanks for your help. I hope for PIC’ers everywhere RTS/CTS ends up being an easy fix :)


Oct 2, 2006 at 5:55pm

I just wanted to gently poke at the situation to see if there was any hope…it’d really help me out…I do see that xon/xoff was added recently…

poke poke :)



Oct 3, 2006 at 12:31am

Sorry to disappoint, but this is going to have to take a back seat to
more pressing development concerns. It’s on a list. Some lists are
more equal than others, though.


Am 02.10.2006 um 19:55 schrieb Sean Stevens:

> I just wanted to gently poke at the situation to see if there was
> any hope…it’d really help me out…I do see that xon/xoff was
> added recently…
> poke poke :)

Oct 3, 2006 at 12:48am

Thanks for the quick reply…I just wanted to make sure it wasn’t forgotten, and it sounds like it wasn’t.

Thanks much, please don’t flame me if I remind about it again in 6 months ;)


Feb 19, 2014 at 2:32pm

Any progress on the responding to handshaking?

I have started a similar thread



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