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ATmega16 датащи(PDF) 155 Page - ATMEL Corporation |
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ATmega16 датащи(HTML) 155 Page - ATMEL Corporation |
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155 / 357 page ![]() 155 2466S–AVR–05/09 ATmega16(L) Receiving Frames with 9 Databits If 9 bit characters are used (UCSZ=7) the ninth bit must be read from the RXB8 bit in UCSRB before reading the low bits from the UDR. This rule applies to the FE, DOR and PE status Flags as well. Read status from UCSRA, then data from UDR. Reading the UDR I/O location will change the state of the receive buffer FIFO and consequently the TXB8, FE, DOR and PE bits, which all are stored in the FIFO, will change. The following code example shows a simple USART receive function that handles both 9-bit characters and the status bits. Note: 1. See “About Code Examples” on page 7. Assembly Code Example (1) USART_Receive: ; Wait for data to be received sbis UCSRA, RXC rjmp USART_Receive ; Get status and 9th bit, then data from buffer in r18, UCSRA in r17, UCSRB in r16, UDR ; If error, return -1 andi r18,(1<<FE)|(1<<DOR)|(1<<PE) breq USART_ReceiveNoError ldi r17, HIGH(-1) ldi r16, LOW(-1) USART_ReceiveNoError: ; Filter the 9th bit, then return lsr r17 andi r17, 0x01 ret C Code Example (1) unsigned int USART_Receive( void ) { unsigned char status, resh, resl; /* Wait for data to be received */ while ( !(UCSRA & (1<<RXC)) ) ; /* Get status and 9th bit, then data */ /* from buffer */ status = UCSRA; resh = UCSRB; resl = UDR; /* If error, return -1 */ if ( status & (1<<FE)|(1<<DOR)|(1<<PE) ) return -1; /* Filter the 9th bit, then return */ resh = (resh >> 1) & 0x01; return ((resh << 8) | resl); } |
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