Post by thread:Why Microchip say: "do not use BSF & BCF on Port P

Hi, can anybody explain me the comment Microchip takes in the sourcefile i2c_low.asm (an554)? ... InitI2CBus_Master: bcf _rp0 movf _portb,w andlw 0xFC ; do not use BSF & BCF on Port Pins movwf _portb ; set SDA & SCL to zero. From Now on, simply play with tris RELEASE_BUS ... Why I should not use BSF & BCF on Port Pins? Is it only recommended in this case to make sure that both pins are zero at the same time? --ThoMo ***************************************************************************** * Thomas Mohaupt e-mail: spam_OUTmohauptTakeThisOuTinformatik.tu-cottbus.de * * Sielower Landstr. 82 03044 Cottbus Tel./Fax(PC): +49 355 701423 * *****************************************************************************

>Why I should not use BSF & BCF on Port Pins? Is it only recommended in this >case to make sure that both pins are zero at the same time? That's one good reason. Another is that the output you are driving is trying to pull your signal in the other direction, and a BSF/BCF does a read before writing (read/modify/write). That would cause you to read the opposite of what you want, change the bit you want changed (a different bit), then write the updated (and partially incorrect) value back to the port. Andy ================================================================== Andy Kunz - Montana Design - 409 S 6th St - Phillipsburg, NJ 08865 Hardware & Software for Industry & R/C Hobbies "Go fast, turn right, and keep the wet side down!" ==================================================================