gex-thesis/ch.unit.1wire.tex

\section{1-Wire Unit}

The 1-Wire unit implements the Dallas Semiconductor's 1-Wire protocol, most commonly used to interface smart thermometers (DS18x20). The protocol is explained in \cref{sec:theory-1wire}.

This unit implements the ROM Search algorithm that is used to find the ROM codes of all 1-Wire devices connected to the bus. The algorithm can find up to 32 devices in one run; more devices can be found by issuing the SEARCH\_CONTINUE command.

Devices are addressed using their ROM codes, unique 64-bit (8-byte) identifiers that work as addresses. When only one device is connected, the value 0 may be used instead and the addressing will be skipped. Its ROM code may be recovered using the READ\_ADDR command or by the search algorithm.

\subsection{1-Wire Configuration}

\begin{inicode}
[1WIRE:ow@7]
# Data pin
pin=A0
# Parasitic (bus-powered) mode
parasitic=N
\end{inicode}

\subsection{1-Wire Commands}

\begin{cmdlist}
	0 & \cname{CHECK\_PRESENCE}
	Test if there are any devices attached to the bus.
	& \begin{cmdresp}
		\cfield{u8} presence detected (0, 1)
	 \end{cmdresp} \\

	1 & \cname{SEARCH\_ADDR}
	Start the search algorithm.
	& \begin{cmdresp}
		\cfield{u8} should continue (0, 1)
		\cfield{u64[]} ROM codes
	 \end{cmdresp} \\

	2 & \cname{SEARCH\_ALARM}
	Start the search algorithm, finding only devices in an alarm state.
	& \begin{cmdresp}
		\cfield{u8} should continue (0, 1)
		\cfield{u64[]} ROM codes
	 \end{cmdresp} \\

	3 & \cname{SEARCH\_CONTINUE}
	Continue a previously started search
	& \begin{cmdresp}
		\cfield{u8} should continue (0, 1)
		\cfield{u64[]} ROM codes
	 \end{cmdresp} \\

	4 & \cname{READ\_ADDR}
	Read a device address (single device only)
	& \begin{cmdresp}
		\cfield{u64} ROM code
	 \end{cmdresp} \\

	10 & \cname{WRITE}
	Write bytes to a device.
	& \begin{cmdreq}
		\cfield{u64} ROM code
		\cfield{u8[]} bytes to write
	\end{cmdreq} \\

	11 & \cname{READ}
	Write a request and read response.
	&
	\begin{cmdreq}
		\cfield{u64} ROM code
		\cfield{u16} read length
		\cfield{u8} verify checksum (0, 1)
		\cfield{u8[]} request bytes
	\end{cmdreq}
	\cjoin
	\begin{cmdresp}
		\cfield{u8[]} read bytes
	\end{cmdresp}
	\\

	20 & \cname{POLL\_FOR\_1}
	Wait for a READY status, used by DS18x20.
	Not available in parasitic mode.
	Responds with SUCCESS after all devices are ready.
	& \\

\end{cmdlist}