Hi Robert.
Re:
I presume, that by 9600 baud you mean 9600 bps. So 1.04ms by 9600
should give 1000. But it gives 10 000. Something is wrong, isn't it ?
No. At 9600 bps, _bits_ are sent out every 1/9600s, or every 104us.
But 1 start bit, 8 data bits and 1 stop bit is 10 bits total,
therefore each _byte_ happens every 104us x 10 = 1.04ms. Therefore
you get a Tx INT every 1.04ms.
So I presume 0.104 ms, which gives 104us.
1.04ms. See above.
With 115200 it is 12 times less, which is around 8us.
with MCLK 7372800 one clock tick i 0.13us
Maybe I don't understand sth, but msp430 is almost close to it's limits!
Cheers
robert
At 115200 bps, a Tx INT happens every 86us (1.04ms / 12). That is of
course much faster than the situation at 9600 bps. Most code that
I've seen that runs at these high rates sends data directly and not
via the ISR, because the overhead of getting into and out of the ISR
is too high. Plus, the characters leave very quickly, so the Tx buff
is usually ready for another very soon thereafter.
regards,
______________________________________
Andrew E. Kalman, Ph.D. [email protected]
There was a long thread on USART TX ints a while back (2 months?)
in the MSP430 Yahoo group.
I posted my Tx USART code, which used a method of controlling
TXIE that solved the problem(s) of the original poster.
Here it is: http://groups.yahoo.com/group/msp430/message/13559
I use it so serve up web pages over TCP/IP on the MSP430 -- so
the strings are quite long, and there are lots of other things
happening while the ISRs are active and sending data. tested at
9600 baud with buffers ranging from 60 to 512 bytes.
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