Uploading fail in RS485 half duplex mode

[mei]

due to UART 2-byte FIFO RX buffer and receive enabled during
transmitting, any data read from UDR may contain
data previously transmitted. Storing program data fails with error:
Too many retry!
Update fail
, but practically only first page of memory is stored.

so I decided to modify transmitting routine of boot loader:

void WriteCom(unsigned char dat)
{
#if RS485
UCSRBREG(COMPORTNo) = (1 << TXENBIT(COMPORTNo));
RS485Enable();
#endif

UDRREG(COMPORTNo) = dat;
//wait send finish
while(!(UCSRAREG(COMPORTNo) & (1<<TXCBIT(COMPORTNo))));
UCSRAREG(COMPORTNo) |= (1 << TXCBIT(COMPORTNo));

#if RS485
UCSRBREG(COMPORTNo) = (1 << RXENBIT(COMPORTNo));
RS485Disable();
#endif
#if WDG_En
//clear watchdog
wdt_reset();
#endif
}

[shao ziyang]

yes, if you using RS485 you may meet this problem.

I often connect RS485's DE and RE, then when you sending data, RE will be disable, so it will not receive data transmtting.

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Best regard

Shaoz...@gmail.com
https://sites.google.com/site/shaoziyang