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Gabriel Caffese
Joined: 09 Oct 2003
Posts: 39
Location: LA PLATA, ARGENTINA
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| About RS485 9th bit |
 Posted: Fri Jan 14, 2005 12:45 pm |
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Hello everyone,
I want to use the 9th bit option the " #use rs232 " command has.
My rs485 network, has 1 master and 16 slaves.
I will use the 9th bit for addressing one device in particular, and all devices will hear and detect it, but can not find the way to do this. There is no example about this 9th bit option. There is one example on RS485 communication, but none about this topic.
Has anyone done such a thing before, and could help me ?
Thanks in advance,
Gabriel.- |
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Mark
Joined: 07 Sep 2003
Posts: 2838
Location: Atlanta, GA
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| Posted: Fri Jan 14, 2005 1:07 pm |
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| Basically you setup for 9 bit data. The nineth bit is set for addresses and clear for data. In your receive interrupt, check the nineth data bit. If it is set, see if the data matches the device address. If not, you can ignore the rest of the data until you see the nineth bit set again. I like to set up the registers myself. So I would read the section in the datasheet to set things up. |
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Gabriel Caffese
Joined: 09 Oct 2003
Posts: 39
Location: LA PLATA, ARGENTINA
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| Posted: Fri Jan 14, 2005 9:47 pm |
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Mark,
I´ve already done what you say, but can not get a clue.
The problem is that I can not detect the 9th bit.
Does anyone have sample code for helping me ?
Thanks.- |
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Ttelmah
Guest
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| Posted: Sat Jan 15, 2005 3:15 am |
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| Gabriel Caffese wrote: | Mark,
I´ve already done what you say, but can not get a clue.
The problem is that I can not detect the 9th bit.
Does anyone have sample code for helping me ?
Thanks.- |
If you want to access the ninth bit directly in CCS, without talking to the registers, then use:
#bit ninth_bit = RS232_ERRORS.7
This then allows you to set the bit, and retrieve the bit when needed. So when a character is received, if you read 'ninth_bit', it will contain the bit received. If you write to 'ninth_bit', and then send a character, the value you wrote, gets sent as the ninth bit.
Best Wishes |
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Gabriel Caffese
Joined: 09 Oct 2003
Posts: 39
Location: LA PLATA, ARGENTINA
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| Posted: Sat Jan 15, 2005 2:31 pm |
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Ttelmah,
At RCSTA.0, I could get that 9th bit I´m looking for (but never appears).
I´m using the hardware UART, so at RS232_ERRORS, there is a copy of RCSTA (except bit 0, wich is used to indicate a parity error).
So, having a hardware UART, I loose that 9th bit (if reading RS232_ERRORS).
If I directly check the RCSTA register, I always see it in 0.
In resume, has anyone managed to use this 9th bit option ???
If so, could you post an example ??
Thanks to everone who helped.
Gabriel.- |
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Mark
Joined: 07 Sep 2003
Posts: 2838
Location: Atlanta, GA
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| Posted: Sat Jan 15, 2005 2:47 pm |
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| Post a small sample test program. One for the send and one for the receive. |
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Thomas Blake
Joined: 18 Jan 2004
Posts: 22
Location: Burbank CA
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| 9th bit |
| Posted: Mon Jan 17, 2005 11:54 am |
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I've used the 9th bit for RS-485 using the PIC16F873:
#BYTE rcsta_copy = 0x0018
#BIT rx_bit_9 = rcsta_copy.0
Originally I did have a problem with using the 16F873.h file macros with PCM 3.092, so I manually put in the #BYTE directive with the RCSTA address. You don't say which chip you're using, but try forcing the assignment like that. |
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Gabriel Caffese
Joined: 09 Oct 2003
Posts: 39
Location: LA PLATA, ARGENTINA
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| Posted: Mon Jan 17, 2005 4:20 pm |
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Thomas,
Thank you very much for replying. I have just solved the problem. It was a PC-software problem -the master- wich was not checked by me.
Now I have done software in Turbo Pascal and everything works ok.
Gabriel.- |
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Ttelmah
Guest
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| Posted: Tue Jan 18, 2005 3:12 am |
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The number of problems with PC communication, caused by things like the MSComm control, is 'legion'...
Glad it is working now.
Best Wishes |
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Goldfrapp
Guest
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| Neither can I........... |
| Posted: Thu Jan 20, 2005 9:58 pm |
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I have the same problem: Can´t get ninth bit over RS485 !!!!!
For those who solved it: could you post same code, please ?
I transmit from PC, and check with a logic analyzer: From PC side, everything is ok.
When receiving from 16F87, I never ever get this ninth bit !!!!
HELP ! |
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Guest
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| Posted: Fri Jan 21, 2005 7:58 am |
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Ooops !
I have the same problem. Help me too !!!! |
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David Lynch
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| Posted: Fri Jan 21, 2005 7:37 pm |
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It seems noone really knows about this.
Maybe would be better to visit the Piclist. Think you should.
David |
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rwyoung
Joined: 12 Nov 2003
Posts: 563
Location: Lawrence, KS USA
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| Posted: Fri Jan 21, 2005 8:50 pm |
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| David Lynch wrote: | It seems noone really knows about this.
Maybe would be better to visit the Piclist. Think you should.
David |
RJ answered the question above very well with
#bit ninth_bit = RS232_ERRORS.7
If your compiler does not support this you can create your own version of RS232_ERRORS with the #byte command at the datasheet for your part, specifically the section on its hardware UART.
If you are trying to do 9-bit transfers with the software UART generated by the CCS compiler, you are going to have problems. Better in this case to write your own software UART if your chip doesn't have a hardware UART.
_________________
Rob Young
The Screw-Up Fairy may just visit you but he has crashed on my couch for the last month! |
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David Lynch
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| Posted: Sat Jan 22, 2005 6:42 am |
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rwyoung,
Think you´re wrong. RS232_ERRORS.7 is only used with software uart. It´s easy that way. Have not heard of anyone that could solve the hardware uart problem.
David. |
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Mark
Joined: 07 Sep 2003
Posts: 2838
Location: Atlanta, GA
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| Posted: Sat Jan 22, 2005 8:58 am |
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From the datasheet:
| Quote: |
RCSTA: RECEIVE STATUS AND CONTROL REGISTER (ADDRESS 18h)
bit 7 SPEN: Serial Port Enable bit
1 = Serial port enabled (configures RC7/RX/DT and RC6/TX/CK pins as serial port pins)
0 = Serial port disabled
bit 6 RX9: 9-bit Receive Enable bit
1 = Selects 9-bit reception
0 = Selects 8-bit reception
bit 5 SREN: Single Receive Enable bit
Asynchronous mode:
Don’t care
Synchronous mode - master:
1 = Enables single receive
0 = Disables single receive
This bit is cleared after reception is complete.
Synchronous mode - slave:
Don’t care
bit 4 CREN: Continuous Receive Enable bit
Asynchronous mode:
1 = Enables continuous receive
0 = Disables continuous receive
Synchronous mode:
1 = Enables continuous receive until enable bit CREN is cleared (CREN overrides SREN)
0 = Disables continuous receive
bit 3 ADDEN: Address Detect Enable bit
Asynchronous mode 9-bit (RX9 = 1):
1 = Enables address detection, enables interrupt and load of the receive buffer when RSR<8> is set
0 = Disables address detection, all bytes are received, and ninth bit can be used as parity bit
bit 2 FERR: Framing Error bit
1 = Framing error (can be updated by reading RCREG register and receive next valid byte)
0 = No framing error
bit 1 OERR: Overrun Error bit
1 = Overrun error (can be cleared by clearing bit CREN)
0 = No overrun error
bit 0 RX9D: 9th bit of Received Data (can be parity bit, but must be calculated by user firmware)
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Bit 0 of the RCSTA is the nineth bit. If you are having problems, then read the datasheet. Quit using the ERRORs variable and do it yourself. And as far as | Quote: | Have not heard of anyone that could solve the hardware uart problem.
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I can  Works just fine when you read and understand the datasheet. |
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