Post by thread:Addressable serial port

I am interested in using a feature that Microchip is promoting as a way to simplify programming of serial comms. for PICs located on a multi-drop network.The 16F87x devices will generate an interrupt when a byte is received with the ninth bit set. The idea is to use the USART in 9 data bit mode where the ninth bit is used to indicate an address. This would greatly simplify programming networked PICs. You just check each address byte to see if it is yours. If it is, just read in the subsequent bytes. Otherwise, just ignore all bytes. In my application, I want to network some number of PICs (at least six to start with) and communicate to them with a PC. The question is: who makes an RS485 card with a USART that has 9 data bits? Paul A. Brown

Company in San Diego, ACCESS-I/O has them--cheapest and best I've found. I also believe SeaLevel in Florida makes one, but have no experience. You can always pay catalog prices and go to B&B or Black-Box or Industrial ComputerSource. I could suggest contacting Rick LeGrande at <spam_OUTrickTakeThisOuTaccess-usa.com>. Tell him Kelly Sent You. There is also a company whose name escapes me at the moment that will sell you the card, the Windows, AND PIC code--but NOT cheap. Really aggressive licensing and fees--to the point of laughter on my part. Client required I use their hardware on a project some years ago. Source disks from the factory had a rather nasty virus, and it was all downhill from there. Don't recommend them. I anticipate doing a similar project with up to 125 such devices spread down a 6-KM long bridge in the next year. Would really like to keep track of your efforts and possibly contribute a bit. At 09:35 AM 9/29/99 -0400, you wrote: {Quote hidden}>I am interested in using a feature that Microchip is promoting as a way to >simplify programming of serial comms. for PICs located on a multi-drop >network.The 16F87x devices will generate an interrupt when a byte is >received with the ninth bit set. The idea is to use the USART in 9 data >bit mode where the ninth bit is used to indicate an address. This would >greatly simplify programming networked PICs. You just check each address >byte to see if it is yours. If it is, just read in the subsequent bytes. >Otherwise, just ignore all bytes. > >In my application, I want to network some number of PICs (at least six to >start with) and communicate to them with a PC. The question is: who makes >an RS485 card with a USART that has 9 data bits? > >Paul A. Brown > > William K. Borsum, P.E. -- OEM Dataloggers and Instrumentation Systems <.....borsumKILLspam@spam@dascor.com> & <http://www.dascor.com>San Diego, California, USA

Check out http://www.hth.com/snap At 09:35 AM 9/29/99 -0400, you wrote: >I am interested in using a feature that Microchip is promoting as a way to >simplify programming of serial comms. for PICs located on a multi-drop >network.The 16F87x devices will generate an interrupt when a byte is >received with the ninth bit set. The idea is to use the USART in 9 data >bit mode where the ninth bit is used to indicate an address. This would >greatly simplify programming networked PICs. You just check each address >byte to see if it is yours. If it is, just read in the subsequent bytes. >Otherwise, just ignore all bytes. > >In my application, I want to network some number of PICs (at least six to >start with) and communicate to them with a PC. The question is: who makes >an RS485 card with a USART that has 9 data bits? > >Paul A. Brown > > Nino -- ****************************************************** * Antonio (Nino) Benci * * Professional Officer / Electronic Services Manager * * Monash University - Dept of Physics * * Wellington Rd, Clayton. 3168 * * Victoria, Australia. * * TEL - 61 3 9905 3649, FAX - 61 3 9905 3637 * * Mobile - 0414 764 763 (private and ah only) * * EMAIL - nino.benciKILLspamsci.monash.edu.au (work) * * - .....fleatechKILLspam.....excite.com (private) * * WWW - http://www.physics.monash.edu.au/ * ******************************************************

Paul, We have successfully completed a similar project very similar to what you describe, using the 'F877. We have 32 PIC-based slave nodes on the RS-485 bus, with the PC as the master. The 9 bit address wake-up feature of the PIC is worthwhile in reducing overhead, and works a treat! In fact, all UARTs operate in "9-bit" mode, that is 8 data bits plus 1 parity bit. If you examine the timing requirements for the PIC you will see that 9th bit used for address wake up sits in the "parity" position on the serial bit stream. Thus addressing a PIC from the PC simply requires setting the parity bit of the PC UART to "mark" for the address byte, thereafter setting the parity bit to "space" for subsequent data bytes of the message to that addressed PIC, and so on. We have provided an external isolated RS-232 to RS-485 convertor plugged into the COM port on the PC side. Hope this helps. BTW, we are running at 19 200, 'twas fine for our application. John Maud Paul Brown wrote: {Quote hidden}> > I am interested in using a feature that Microchip is promoting as a way to > simplify programming of serial comms. for PICs located on a multi-drop > network.The 16F87x devices will generate an interrupt when a byte is > received with the ninth bit set. The idea is to use the USART in 9 data > bit mode where the ninth bit is used to indicate an address. This would > greatly simplify programming networked PICs. You just check each address > byte to see if it is yours. If it is, just read in the subsequent bytes. > Otherwise, just ignore all bytes. > > In my application, I want to network some number of PICs (at least six to > start with) and communicate to them with a PC. The question is: who makes > an RS485 card with a USART that has 9 data bits? > > Paul A. Brown

You can use the PC RS232 port for 9 bit data mode. Use the Parity bit but Program it for Mark or Space to transmit Address or Data. Use the parity error bit to distinguish between Address & Data bytes received. The Parity state bit should always be set the same state during idle time & probably receive time. You will probably need to write your own interupt service routine to handle the parity differently. If you use interupts they will be generated for every byte recived, this means that the PC will have to disgard non relevent bytes. The good thing about reciving every byte is you can use the PC as a bus monitor/diagnostics or node emulator (even multiple nodes). Regards Peter Wintulich EraseMEpwintulispam_OUTTakeThisOuTmicrobits.com.au

Paul Brown wrote: > The question is: who makes an RS485 card with a USART that has 9 data > bits? Umm, all of them IIRC! It's called "parity" and can be set as "stuck" to "mark" or "space". You set the receiver similarly and it signals a parity error when it detects parity contrary to the current setting (as it always does). The difficulty in this method is that it must be set up before sending the character and only that character sent, waiting for the transmitter to fully empty before setting an alternate "parity" and sending further data. But - it's do-able. -- Cheers, Paul B.

This is a fine solution if you want the computer to snoop the RS-485 bus all the time, but if you want it to become an addressable node on the network, you need to design a RS232 to RS485 converter according to your network protocol specifications. That's what I've done to use dumb terminals as network nodes for monitoring and configuring our devices. Thiago Turchetti Maia Di-elitrons Eletrtnica Industrial Ltda. http://www.di-eletrons.com.br/ -----Mensagem original----- {Quote hidden}>De: John Maud <maudspam_OUTIAFRICA.COM> >Para: @spam@PICLISTKILLspamMITVMA.MIT.EDU <KILLspamPICLISTKILLspamMITVMA.MIT.EDU> >Data: Quarta-feira, 29 de Setembro de 1999 22:15 >Assunto: Re: Addressable serial port - 9 data bit RS485 > > >>Paul, >> >>We have successfully completed a similar project very similar to what >>you describe, using the 'F877. We have 32 PIC-based slave nodes on the >>RS-485 bus, with the PC as the master. The 9 bit address wake-up >>feature of the PIC is worthwhile in reducing overhead, and works a >>treat! >> >>In fact, all UARTs operate in "9-bit" mode, that is 8 data bits plus 1 >>parity bit. If you examine the timing requirements for the PIC you will >>see that 9th bit used for address wake up sits in the "parity" position >>on the serial bit stream. Thus addressing a PIC from the PC simply >>requires setting the parity bit of the PC UART to "mark" for the address >>byte, thereafter setting the parity bit to "space" for subsequent data >>bytes of the message to that addressed PIC, and so on. >> >>We have provided an external isolated RS-232 to RS-485 convertor plugged >>into the COM port on the PC side. >> >>Hope this helps. >> >>BTW, we are running at 19 200, 'twas fine for our application. >> >>John Maud >> >>Paul Brown wrote: >>> >>> I am interested in using a feature that Microchip is promoting as a way >to >>> simplify programming of serial comms. for PICs located on a multi-drop >>> network.The 16F87x devices will generate an interrupt when a byte is >>> received with the ninth bit set. The idea is to use the USART in 9 data >>> bit mode where the ninth bit is used to indicate an address. This would >>> greatly simplify programming networked PICs. You just check each address >>> byte to see if it is yours. If it is, just read in the subsequent bytes. >>> Otherwise, just ignore all bytes. >>> >>> In my application, I want to network some number of PICs (at least six to >>> start with) and communicate to them with a PC. The question is: who >makes >>> an RS485 card with a USART that has 9 data bits? >>> >>> Paul A. Brown >