Strange behaviour of SCI transmitter

Posted on August 20, 2005 at 10:59

Hi,

I am working with ST72F264 micro.

The reset value of the SCISR register is 0xC0 which means that TDRE=1, TC=1.

Without clearing the TDRE bit I write into the SCIDR register and it causes immediate SCI transmittion, but in the datasheet it says ''Note: Data will not be transferred to the shift register unless the TDRE bit is cleared.''

can anyone explain this behaviour ?

Basically I want to get an interrupt when transmittion is complete TC=1 to disable my RS232 driver.

Posted on August 22, 2005 at 05:35

Hi Gilat,

did you note that TDRE is cleared by a software sequence (an access to the SR register followed by a write to the DR register) ?

Posted on August 22, 2005 at 05:53

Yes, I did note that but I didn't perform any access to the SR.

I added the SR to the watch window, maybe that's the reason?