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85 lignes
2.3 KiB
85 lignes
2.3 KiB
\section{1-Wire Unit}
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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}.
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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.
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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.
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\subsection{1-Wire Configuration}
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\begin{inicode}
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[1WIRE:ow@7]
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# Data pin
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pin=A0
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# Parasitic (bus-powered) mode
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parasitic=N
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\end{inicode}
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\subsection{1-Wire Commands}
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\begin{cmdlist}
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0 & \cname{CHECK\_PRESENCE}
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Test if there are any devices attached to the bus.
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& \begin{cmdresp}
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\cfield{bool} presence detected
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\end{cmdresp} \\
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1 & \cname{SEARCH\_ADDR}
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Start the search algorithm.
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& \begin{cmdresp}
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\cfield{bool} should continue
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\cfield{u64[]} ROM codes
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\end{cmdresp} \\
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2 & \cname{SEARCH\_ALARM}
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Start the search algorithm, finding only devices in an alarm state.
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& \begin{cmdresp}
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\cfield{bool} should continue
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\cfield{u64[]} ROM codes
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\end{cmdresp} \\
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3 & \cname{SEARCH\_CONTINUE}
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Continue a previously started search
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& \begin{cmdresp}
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\cfield{bool} should continue
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\cfield{u64[]} ROM codes
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\end{cmdresp} \\
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4 & \cname{READ\_ADDR}
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Read a device address (single device only)
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& \begin{cmdresp}
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\cfield{u64} ROM code
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\end{cmdresp} \\
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10 & \cname{WRITE}
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Write bytes to a device.
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& \begin{cmdreq}
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\cfield{u64} ROM code
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\cfield{u8[]} bytes to write
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\end{cmdreq} \\
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11 & \cname{READ}
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Write a request and read response.
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&
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\begin{cmdreq}
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\cfield{u64} ROM code
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\cfield{u16} read length
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\cfield{bool} verify checksum
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\cfield{u8[]} request bytes
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\end{cmdreq}
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\cjoin
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\begin{cmdresp}
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\cfield{u8[]} read bytes
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\end{cmdresp}
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\\
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20 & \cname{POLL\_FOR\_1}
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Wait for a READY status, used by DS18x20.
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Not available in parasitic mode.
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Responds with SUCCESS after all devices are ready.
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& \\
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\end{cmdlist}
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