SH7043 Maximum baud rate

Hi all,

I am having problems using the Hitachi SH7043 for RS232 communication
beyond 38400 Kbps. ( I keep getting Overrun Errors).

I suspect that the UART's reliable communication limit is 38400Kbps

Any help would be greatly appreciated.

Thanks in advance,
Vivek

"vivek" <vivek.seetharaman@wipro.com> wrote in message 
news:1128504668.499362.97170@g14g2000cwa.googlegroups.com...
> I am having problems using the Hitachi SH7043 for RS232 communication
> beyond 38400 Kbps. ( I keep getting Overrun Errors).
>
> I suspect that the UART's reliable communication limit is 38400Kbps
>
I have had no trouble running a 7043 at 115Kbd, but that was using 
interrupts. If you are using polling to check for characters received you 
need to be sure that your code checks back before the next character is 
received.

Stan 

Thanks so much for your prompt reply, Stan.
I'm using interrupts as well. I am able to send data at 115Kbps
successfilly but
reception of chunks of data(say 1k) eventually results in an Overrun
error.

>From my understanding, the SH7043 has UART\SCI with a single byte
hardware
buffer. I was under the impression that because the SCI does not have a
FIFO queue for buffering, high baud rates would be unreliable.

But the fact that you are able to communicate at 115Kbps suggests that
my understanding is incorrect. I will go back and try to figure this
out.

I would greatly appreciate any advice that you can offer.

Thanks again !
Vivek

vivek wrote:

> Thanks so much for your prompt reply, Stan.
> I'm using interrupts as well. I am able to send data at 115Kbps
> successfilly but
> reception of chunks of data(say 1k) eventually results in an Overrun
> error.
>
> >From my understanding, the SH7043 has UART\SCI with a single byte
> hardware
> buffer. I was under the impression that because the SCI does not have a
> FIFO queue for buffering, high baud rates would be unreliable.
>
> But the fact that you are able to communicate at 115Kbps suggests that
> my understanding is incorrect. I will go back and try to figure this
> out.
>
> I would greatly appreciate any advice that you can offer.
>
> Thanks again !
> Vivek

Even when interrupts are used, there are some possible traps:
* Are there any other, higher-priority interrupts that run for a
significant amount of time?
* Are there lower-priority interrupts that "forget" to re-enable
interrupts at the beginning of the interrupt routine?
* Are there critical sections in the code that turn off interrupts?

Any of these can cause interrupt handling to be delayed long enough for
characters to be missed.

Anyway, there is a solution. Like many other Renesas chips, the 7043
contains a DTC (Data Transfer Controller). The DTC can push data in the
background, without generating an interrupt.You can, for example,
program the DTC to push serial data into a ring buffer, which you poll
periodically.

Thanks Hans! Appreciate the help.