Is there a requirement to delay using the USART (at least for asynchronous transmission) for a period of time after initially setting it up and enabling interupts until transmitting the first character? I ask, because when I set it up and then immediately use it to output a character (or string of characters), they are consistently wrong. I tried outputing the following string: "sys initialised". If I do this immediately after the setting up, I get (consistently) the output on the right (see below). However, if I wait for 128 microseconds (gcc _delay_loop_1(255)), I sometimes get the correct output and sometimes the wrong output (about 20% of the time, it's wrong). If I wait for approx. 43ms (gcc _delay_loop_2(65535)), then I seem to get the correct result each time I 'boot' my system. The ATmega8535 datasheet does not seem to say that a delay is required. The system runs in an infinite loop but uses interupts to write the characters from a software circular buffer into the USART. Each time the USART signals that its own buffer is empty, then the data from the circular buffer is transferred to the UDR a character at a time. The necessity for this delay was not noticed before, since the previous owner of the project was writting some stuff to eeprom before outputting the first USART character and the problem didn't show - except occasionally I did notice some corrupted characters being output at startup. The system does have 2 DC motors that spin for less than a second as power is applied until the I/O ports are set up, but the wrong column is always the same data - so, I don't think it is noise. The system is running with a 6.000MHz crystal with the external clock pin enabled. I'm using: 1200baud, 8-bits, 1 stop, no parity. (binary representation given because there are patterns that can be detected - the right side of the 'wrong' columns are generally the same as the left side of the 'correct' columns.) correct wrong 01110011 10101110 01111001 10101111 01110011 00101110 00100000 10100100 01101001 01011010 01101110 00101011 01101001 10001011 01110100 10100101 01101001 10000101 01100001 10110001 01101100 10100101 01101001 11001101 01110011 10010101 01100101 10010001 01100100 11111101 Anyone got any suggestions or observations? Thanks.
ATmega8535 and USART post-initialisation delay required?
Started by ●March 13, 2005
Reply by ●March 13, 20052005-03-13
Reply by ●March 16, 20052005-03-16
U�ytkownik "Joe" <ffffh.no.spam@hotmail-spammers-paradise.com> napisa� w wiadomo�ci news:d11ulf$umv$1@news7.svr.pol.co.uk...> correction: > with the short delay, it is CORRECT 20% of the time. > > >I also needed delay when slave, (ATmega32) responsed to master, ( PC ) by rs485 wire. In my case it was coused by fact that other side of rs cable (PC) didn't manage to switch back to recive mode fast enough Michal M..
Reply by ●March 17, 20052005-03-17
the setup is a normal RS232 serial port - not a master/slave setup. "Michal Machowski" <machowsk@interia.pl> wrote in message news:d1b8to$mtj$1@nemesis.news.tpi.pl...> > U�ytkownik "Joe" <ffffh.no.spam@hotmail-spammers-paradise.com> napisa� w > wiadomo�ci news:d11ulf$umv$1@news7.svr.pol.co.uk... > > correction: > > with the short delay, it is CORRECT 20% of the time. > > > > > > > I also needed delay when slave, (ATmega32) responsed to master, ( PC ) by > rs485 wire. > In my case it was coused by fact that other side of rs cable (PC) didn't > manage to switch back to recive mode fast enough > Michal M.. > >
