9 Bit Transmission

[Pesticida]

Hi,

Thank You !

Yes I think I will use my own Protocoll !

But I dont understand how Can I send a 9 Bit Packet when a Byte have just 8 Bit?

9 Bit is more then 255 and is a Word Size !

Thats mean when I Use 9Th Bit I must send a Word Divided in two Bytes ?

Thanks

Regard Pesti.

[Jerson]

Pesti

You do not have to use 9 bits. Your standard serial UART will do the job just fine. I mentioned this earlier

You can define your own protocol and use it with normal 8 bit data.

When you use the 9 bit packets, you distinguish address and data bytes by the 9th bit alone. So, any byte having the 9th bit set is an 8bit address byte whereas all words with the 9th bit low are data.

Jerson

[Pesticida]

Ok I understand,but where is the 9th bit ?

When I send 1 Byte I have: 1 Start Bit,8 Data Bit,1 Stop Bit.
Where Is here the 9Th Bit? :-)

For example when I use Hyperterminal I can not adjust to 9th Bit I just have 7 or 8 Bit data.

Regard Pesti

[Luciano]

Hi,

The USART module of a PIC has multi-processor communication
capability using 9-bit address detection.

See this document:
http://www.datadog.com/rs485.pdf

Use The PC's UART With 9-Bit Protocols
http://www.elecdesign.com/Articles/I...ArticleID=6245
(You will have to wait 20 seconds before you see the doc).

See the datasheet of the used chip.

Best regards,

Luciano

[Pesticida]

Mille Grazie Luciano !

:-)

Regard Pesti

[Luciano]

Hi Pesti,

With the VB MScomm control you can set the parity as following:

Setting   Description 
E         Even 
M         Mark 
N         (Default) None 
O         Odd 
S         Space

If you use MARK parity, then the bit after the data word is a logical 1.
If you use SPACE parity, then the bit after the data word is a logical 0.

With MARK parity the slave device will see the data as a 9-bit transmission. (Last bit = 1)
Use the MARK parity to send the address to the slaves.

With SPACE parity the slave device will see the data as a 9-bit transmission. (Last bit = 0)
Use SPACE parity to send the data to the selected slave.


(Click on the picture to enlarge)

(VB pseudocode)

VB pseudocode
.....
Insert a delay here to ensure that UART FIFO buffer of the PC is 
empty before you change the parity. The UART 16550 has up to 16 bytes 
for the FIFO transmit buffer. 

MSComm.Settings = "9600,M,8,1"
MSComm.Output = (The slave Address) 

Insert a delay here to ensure that UART FIFO buffer of the PC is 
empty before you change the parity. The UART 16550 has up to 16 bytes 
for the FIFO transmit buffer. 

MSComm.Settings = "9600,S,8,1"
MSComm.Output = (The data for the selected slave)
.....

From the Windows control panel you can adjust the size of the FIFO buffers of the used serial port.

(Click on the picture to enlarge)

Best regards,

Luciano

[Pesticida]

Hi,

Thank You!

Thats it !
This is the Answer what I waiting for.

Now I know how to Programming the Software routines.

I use Pic 18f452 and I see on the PDF Datasheet that I can set the 9th Bit Transmission for RX and TX.

Thanks a lot Luciano!

Buona Giornata!


Regard Pesti.