From: Laurent P. <lau...@sk...> - 2008-03-17 20:53:09
|
Hi everybody, I'd like to use a Gumstix-based computer as a central processing unit in a multidrop system. All components in the system communicate through an RS485 bus, so I'm looking for solutions to provide RS485 connectivity to the Gumstix board. The RS485 bus transceivers can be connected directly to one of the Gumstix serial ports but require a direction control signal. Some UARTs support automatic direction control using the RTS signal. Even though at least one serial port of the Gumstix supports RTS/CTS, it seems those signals can only be used for flow control and not for direction control. Is that right ? Has any of you connected a Gumstix-based computer to a RS485 bus ? What kind of solution have you used ? I would like to find a solution that can easily be integrated in a custom expansion board. Thanks in advance for any help you can provide. Best regards, Laurent Pinchart |
From: Terry K. <kl...@kl...> - 2008-03-17 21:31:38
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FWIW I have used these (with associated A-D , I/O)... http://www.icpdas.com/products/Remote_IO/i-7000/i-7520.htm 2 wire RS232 from gumstix, autobaud, bus timing etc on RS485 side - no probs. an off the shelf 232 - 485 converter will take away a lot of development pain. As far as the Gumstix software knows its just RS232. Although it is bigger than the gumstix ;) Terry On Mon, 2008-03-17 at 22:00 +0100, Laurent Pinchart wrote: > Hi everybody, > > I'd like to use a Gumstix-based computer as a central processing unit in a > multidrop system. All components in the system communicate through an RS485 > bus, so I'm looking for solutions to provide RS485 connectivity to the > Gumstix board. > > The RS485 bus transceivers can be connected directly to one of the Gumstix > serial ports but require a direction control signal. Some UARTs support > automatic direction control using the RTS signal. Even though at least one > serial port of the Gumstix supports RTS/CTS, it seems those signals can only > be used for flow control and not for direction control. Is that right ? > > Has any of you connected a Gumstix-based computer to a RS485 bus ? What kind > of solution have you used ? I would like to find a solution that can easily > be integrated in a custom expansion board. > > Thanks in advance for any help you can provide. > > Best regards, > > Laurent Pinchart > > ------------------------------------------------------------------------- > This SF.net email is sponsored by: Microsoft > Defy all challenges. Microsoft(R) Visual Studio 2008. > http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/ > _______________________________________________ > gumstix-users mailing list > gum...@li... > https://lists.sourceforge.net/lists/listinfo/gumstix-users > > |
From: Laurent P. <lau...@sk...> - 2008-03-17 21:40:36
|
Hi Terry, On Monday 17 March 2008, Terry Kemp wrote: > FWIW I have used these (with associated A-D , I/O)... > http://www.icpdas.com/products/Remote_IO/i-7000/i-7520.htm Thanks for the information. > 2 wire RS232 from gumstix, autobaud, bus timing etc on RS485 side - no > probs. > > an off the shelf 232 - 485 converter will take away a lot of development > pain. As far as the Gumstix software knows its just RS232. > > Although it is bigger than the gumstix ;) That's the main problem with most of these modules (along with the price and the external power supply). I would like to find a solution that I could integrate on a custom expansion board with as little components as possible. Best regards, Laurent Pinchart |
From: Robert F. <ro...@fa...> - 2008-03-17 21:53:06
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I use rs485 with an ftdi chip 2232 at 1 megabaud. The only down side is usb latency. To minimize this I don't use the ftdi sio driver but instead use the ftdilib. Latency with ftdilib gets to 8ms. -----Original Message----- From: gum...@li... [mailto:gum...@li...] On Behalf Of Terry Kemp Sent: Monday, March 17, 2008 5:32 PM To: General mailing list for gumstix users. Subject: Re: [Gumstix-users] Gumstix and RS485 connectivity FWIW I have used these (with associated A-D , I/O)... http://www.icpdas.com/products/Remote_IO/i-7000/i-7520.htm 2 wire RS232 from gumstix, autobaud, bus timing etc on RS485 side - no probs. an off the shelf 232 - 485 converter will take away a lot of development pain. As far as the Gumstix software knows its just RS232. Although it is bigger than the gumstix ;) Terry On Mon, 2008-03-17 at 22:00 +0100, Laurent Pinchart wrote: > Hi everybody, > > I'd like to use a Gumstix-based computer as a central processing unit in a > multidrop system. All components in the system communicate through an RS485 > bus, so I'm looking for solutions to provide RS485 connectivity to the > Gumstix board. > > The RS485 bus transceivers can be connected directly to one of the Gumstix > serial ports but require a direction control signal. Some UARTs support > automatic direction control using the RTS signal. Even though at least one > serial port of the Gumstix supports RTS/CTS, it seems those signals can only > be used for flow control and not for direction control. Is that right ? > > Has any of you connected a Gumstix-based computer to a RS485 bus ? What kind > of solution have you used ? I would like to find a solution that can easily > be integrated in a custom expansion board. > > Thanks in advance for any help you can provide. > > Best regards, > > Laurent Pinchart > > ------------------------------------------------------------------------- > This SF.net email is sponsored by: Microsoft > Defy all challenges. Microsoft(R) Visual Studio 2008. > http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/ > _______________________________________________ > gumstix-users mailing list > gum...@li... > https://lists.sourceforge.net/lists/listinfo/gumstix-users > > ------------------------------------------------------------------------- This SF.net email is sponsored by: Microsoft Defy all challenges. Microsoft(R) Visual Studio 2008. http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/ _______________________________________________ gumstix-users mailing list gum...@li... https://lists.sourceforge.net/lists/listinfo/gumstix-users |
From: Laurent P. <lau...@sk...> - 2008-03-17 22:55:02
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Hi Robert, On Monday 17 March 2008, Robert Farrell wrote: > I use rs485 with an ftdi chip 2232 at 1 megabaud. The only down side is > usb latency. To minimize this I don't use the ftdi sio driver but instead > use the ftdilib. Latency with ftdilib gets to 8ms. Thanks for the information. The latency is unfortunately a bit high for my application. Most data packets on the RS485 bus will be less than 10 bytes long, and the protocol is based on a request-respond model. Best regards, Laurent Pinchart |
From: Dave H. <dhy...@gm...> - 2008-03-17 22:01:49
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Hi Laurent, > I'd like to use a Gumstix-based computer as a central processing unit in a > multidrop system. All components in the system communicate through an RS485 > bus, so I'm looking for solutions to provide RS485 connectivity to the > Gumstix board. > > The RS485 bus transceivers can be connected directly to one of the Gumstix > serial ports but require a direction control signal. Some UARTs support > automatic direction control using the RTS signal. Even though at least one > serial port of the Gumstix supports RTS/CTS, it seems those signals can only > be used for flow control and not for direction control. Is that right ? > > Has any of you connected a Gumstix-based computer to a RS485 bus ? What kind > of solution have you used ? I would like to find a solution that can easily > be integrated in a custom expansion board. Like Terry, I've used one of t the FTDI to do this. But I've also done it from the robostix with no additional hardware. I'll describe the technique I used on the robostix, since I believe that the same technique could be used on the gumstix. You can connect the Tx from the gumstix to the Rx from the gumstix, and to the RS485 bus. When you're not transmitting, you configure the Tx pin as a GPIO input pin, and the Rx gets all of the data. When you want to transmit you configure it back to being a Tx pin, send your data and then convert it back to an input pin. The trick is getting the timing right, which would probably require a driver mod. You could also probably play games with the RxD line by configuring it as a GPIO while you're transmitting, then you wouldn't see your own transmission, although seeing your own transmission could be used to turn off the transmitter. -- Dave Hylands Vancouver, BC, Canada http://www.DaveHylands.com/ |
From: Laurent P. <lau...@sk...> - 2008-03-17 22:50:20
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Hi Dave, On Monday 17 March 2008, Dave Hylands wrote: > Hi Laurent, > > > I'd like to use a Gumstix-based computer as a central processing unit in > > a multidrop system. All components in the system communicate through an > > RS485 bus, so I'm looking for solutions to provide RS485 connectivity to > > the Gumstix board. > > > > The RS485 bus transceivers can be connected directly to one of the > > Gumstix serial ports but require a direction control signal. Some UARTs > > support automatic direction control using the RTS signal. Even though at > > least one serial port of the Gumstix supports RTS/CTS, it seems those > > signals can only be used for flow control and not for direction control. > > Is that right ? > > > > Has any of you connected a Gumstix-based computer to a RS485 bus ? What > > kind of solution have you used ? I would like to find a solution that can > > easily be integrated in a custom expansion board. > > Like Terry, I've used one of t the FTDI to do this. But I've also done > it from the robostix with no additional hardware. I'll describe the > technique I used on the robostix, since I believe that the same > technique could be used on the gumstix. > > You can connect the Tx from the gumstix to the Rx from the gumstix, > and to the RS485 bus. > > When you're not transmitting, you configure the Tx pin as a GPIO input > pin, and the Rx gets all of the data. > > When you want to transmit you configure it back to being a Tx pin, > send your data and then convert it back to an input pin. > > The trick is getting the timing right, which would probably require a > driver mod. > > You could also probably play games with the RxD line by configuring it > as a GPIO while you're transmitting, then you wouldn't see your own > transmission, although seeing your own transmission could be used to > turn off the transmitter. There are inexpensive RS485 transceivers that I will probably use to convert from CMOS/TTL levels on the Gumstix side to RS485 on the bus side. The only problem is that the transceiver has a direction control input that I must drive from the Gumstix side. Some UARTs have an Auto-RS485 mode that outputs the data direction signal on the RTS pin. Unfortunately the PXA UARTs don't seem to have that capability. As you noted the tricky part is to get the direction control signal timings right. I'm a bit scared of handling that in software as I need very fast response time to transmit data at 115.2 kbds. I will probably use a very small external microcontroller to perform that task. Programmable logic would have been nicer, but CPLDs have more complex power requirements. Best regards, Laurent Pinchart |