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In lugnet.robotics.nxt, <dickswan@sbcglobal.net> wrote:
>
> I've looked at implementing an interface for RobotC, but I've always
> struggled with why bother since there are no applications that connect
> to it.
>
> I wish LEGO had implemented an option to provide a logic level "RS-232"
> UART on port four. Yes, I know RS-232 defines +/-12V signal levels, but
> there are many devices out there that, except for using logic voltage
> levels, are identical to RS-232. This includes video cameras (CMUCAM,
> AVRCAM) and a wide range of sensor MUXes, servo controller MUXes, GPS,
> etc.
>
> It looks like it would have been very simple to implement an additional
> option for a logic-level serial link with some minor re-arrangement of
> the existing I/O pins already used by sensor port 4.
>
> You can't simply shift the RS-485 signals back to logic level because
> RS-485 is half-duplex and it's not easy to tell the direction of
> transmission. Most of the devices mentioned above require full-duplex
> links. A full duplex link would make it easier to interface to many of
> the devices mentioned above.
>
> LEGO has defined baud rate of 921,600 bps for the RS-485 link. But since
> any application is going to require custom firmware, this could easily
> be changed to whatever you want within the hardware capabilities.
>
> The one application that I can think of is connecting two (or more) NXTs
> together. This would give similar capabilities to that available via
> existing Bluetooth but at a higher bandwidth and much lower latency.
>
> -----Original Message-----
> From: news-gateway@lugnet.com [mailto:news-gateway@lugnet.com] On Behalf
> Of John Barnes
> Sent: Sunday, April 08, 2007 9:20 AM
> To: lugnet.robotics.nxt@lugnet.com
> Subject: Re: Using NXT Port 4 EIA-485
>
> In lugnet.robotics.nxt, Christian Mock wrote:
> > Hi,
> > is there currently any software-support (pbLua, NXT-G, NXJ) for NXT Port4 highspeed serial communication (EIA-485)?
> > Thanks for more informations
> > Christian
>
> As far as I know, there isn't any support for this interface (RS-485
> sensor port 4) in either the standard firmware or any of the other third
> party firmware implementations.
>
> The interface runs at 921,600 bps so it will be fast enough to be really
> useful. I am hoping that, eventually, it will be supported.
> JB
Hi,
halfduplex is not the problem when connecting the NXT to an external MCU.
My problem is the bitrate of 921,6 kbits/s. Simple cheap MCU like ATMega didn't
support this bitrate (as far as I know).
To add an external devices (e.g MCU+SD-Card or MCU+serial camera ) to NXT, it
seems to be neccessary to implement the P-Net-Protocol (http://www.p-net.org).
Is this protocol allways used when using Port4 highspeed communication ?
Thanks for more information
Bye
Christian
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