Developing frames/packets using serial data (bytes)

samurai · Joined: 15 Apr 2008 Posts: 1

Hi guys,

I'm using PIC16F877A for a LED display.
The PIC communicates with a PC using the serial port.
Here PC will send binary data (ex: data that should be displayed in the LED display).

I'm thinking of below scenario to send data from PC to PIC.

PC send below frame to PIC.

StartFlag-DataLength-Data-StopFlag
| | | |
1byte 2bytes xbyte 1byte

someone pls advice me on how to do this.

reg.

RLScott · Joined: 10 Jul 2007 Posts: 465

Whenever you have a connection that could be broken, it is good to have a protocol in place to re-establish synchronization in the event that it is lost. Therefore I suggest that you make your StartFlag unique - so that it can never appear in the DataLength, Data, or StopFlag. That means your DataLength would not be straight binary, which could attain any value, but rather it would be encoded in some way to avoid the StartFlag value. The same consideration should be followed for the Data field. One way to do this would be to send 4 bits in each character. Or, if you want to be more efficient, send 7 bits in each character and use bit 7 to indicate that the character is a StartFlag or StopFlag.

Robert Scott
Real-Time Specialties