On Tue, 19 Mar 2013 09:08:26 -0700 (PDT), you wrote:

>I am trying to transfer 256 bytes of at data 1M baud rate from my PC to an=
 Atmega328 microcontroller. I am using checksum to verify the integrity of =
the data and I am emptying the received data into a ring buffer as quickly =
as possible. This is all I have in my interrupt subroutine:
>temp =3D UDR0;
>BufferWrite(&rx_buffer,&temp);=20
>The data is transferred properly only at speeds upto 250K baud rate. It re=
sults in error beyond that point. The Atmega 328 datasheet specifies that i=
t possible to transfer at speeds upto 2M baud rate. The ring buffer size is=
 about 400 bytes and I am looking for some suggestions to achieve higher ba=
ud rates while maintaining the data integrity.
>Sai

The ATMEGAs can do these rates but you need to look carefully  at the assem=
bler that your compiler
is generating for the ISR code to check timings are adequate - add an IO po=
rt set/reset around your
ISR code to check how long it's taking on a scope.=20

You also need the data to be clean- certainly not via an RS232 driver - nee=
ds to be 5V TTL UART
(e.g. from USB-serial chip located nearby) or RS422/485does the waveform lo=
ok OK on the scope?

If transfer is on the edge, adding an extra stop bit can help, but you need=
 to have an understanding
of exactly what is happenning and why it is failing.


--=20
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