Appendix C – 1-Wire Communications

Appendix C – 1-Wire Communications 1-Wire Communications The 1-Wire protocol was developed by Dallas Semiconductor to communicate with chips using a single signalling line. This implementation was written for MMBasic by Gerard Sexton. There are three commands that you can use: ONEWIRE RESET pin ONEWIRE WRITE pin, flag, length, data [, data…] ONEWIRE READ pin, flag, length, data [, data…]

Reset the 1-Wire bus Send a number of bytes Get a number of bytes

Where: pin - The I/O pin to use. It can be any pin capable of digital I/O. flag - A combination of the following options: 1 - Send reset before command 2 - Send reset after command 4 - Only send/recv a bit instead of a byte of data 8 - Invoke a strong pullup after the command (the pin will be set high and open drain disabled) length - Length of data to send or receive data - Data to send or variable to receive. The number of data items must agree with the length parameter. The automatic variable MM.ONEWIRE returns true if a device was found After the command is executed, the I/O pin will be set to the not configured state unless flag option 8 is used. When a reset is requested the automatic variable MM.ONEWIRE will return true if a device was found. This will occur with the ONEWIRE RESET command and the ONEWIRE READ and ONEWIRE WRITE commands if a reset was requested (flag = 1 or 2). The 1-Wire protocol is often used in communicating with the DS18B20 temperature measuring sensor and to help in that regard MMBasic includes the TEMPR() function which provides a convenient method of directly reading the temperature of a DS18B20 without using these functions.