Post by thread:[PIC]: USART first (dummy) byte problem

Hello all, I am using a 16F873 and have a working interrupt driven asynchronous 1/2 duplex USART with one problem. I preload the TXREG with FFh as a dummy character. When TXEN is set and the PIC transmits the FFh, I get an error in the receiving device. It appears on the scope as if the baud rate changes during the transmission of the first character. I have used a W9x app to receive the dummy char as well as another embedded (HC12) product. I have loaded TXSTA with a literal word as well as set bits individually as shown below with no difference. Has anyone seen this situation before? ;TXREG preloaded with FFh init_serial: BSF STATUS, RP0 ;Select bank 1 ;Using XTAL of 10.0000 MHz, BRGH=1: movlw Baud38400 ;Select baud rate movwf SPBRG ; / BSF TXSTA,BRGH ;High speed BSF RCSTA,SPEN ;Serial port enable BSF STATUS, RP0 ;Select bank 1 BSF PIE1,RCIE ;Enable receive interrupt BCF STATUS, RP0 ;Select bank 0 BSF RCSTA,CREN ;Enable Continuous Receiving BSF STATUS, RP0 ;Select bank 1 BSF TXSTA,TXEN ;enable transmit in serial port John Gerthoffer Software Engineer American Auto-Matrix, Inc. Smart Building Solutions 724/733-2000 x342 -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]: PIC only [EE]: engineering [OT]: off topic [AD]: advertisements

John Gerthoffer wrote: > > Hello all, > > I am using a 16F873 and have a working interrupt driven asynchronous 1/2 > duplex USART with one problem. I preload the TXREG with FFh as a dummy > character. When TXEN is set and the PIC transmits the FFh, I get an error > in the receiving device. It appears on the scope as if the baud rate > changes during the transmission of the first character. I don't know if this is the case in your code but... Don't try enabling the serial port and immediately send a byte when powering up the chip. I have had many errors if it is done this way. Try placing a small power up delay loop in your code before and after enabling the serial port. Sometimes it takes a little while for the port pins to stabilise. -- Best regards Tony ICmicro's http://www.picnpoke.com spam_OUTsalesTakeThisOuTpicnpoke.com -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.