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77 lignes
2.5 KiB
77 lignes
2.5 KiB
\section{SIPO (Shift Register) Unit}
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The shift registers driver unit is designed for the loading of data into \gls{SIPO} shift registers, such as 74xx4094 or 74xx595. These are commonly used to control segmented \gls{LED} displays, \gls{LED} user interfaces, etc.
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\noindent
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A SIPO shift register has the following digital pins:
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\begin{itemize}[itemsep=0pt]
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\item \textit{Shift} -- \gls{SCK}; shifts the data in the register by one bit
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\item \textit{Data In} -- \gls{MOSI}; serial data to load into the register
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\item \textit{Data Out} -- output for daisy-chaining with other shift registers
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\item \textit{Store} -- latches the current register data and shows it at the outputs
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\item \textit{Clear} -- erases the latched data and clears the display
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\end{itemize}
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This unit automatically handles both the \textit{Shift} and \textit{Store} signals, provides access to the \textit{Clear} output, and is capable of loading multiple shift registers in parallel (an arrangement sometimes used instead of daisy-chaining). The polarity (active level) of all signals can be configured.
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It is, additionally, possible to set the data lines to arbitrary ``idle'' level(s) before sending the \textit{Store} pulse; this may be latched and used for some additional feature on the user interface, such as a brightness control.
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\subsection{SIPO Configuration}
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\begin{inicode}
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[SIPO:display@9]
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# Shift pin & its active edge (1-rising,0-falling)
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shift-pin=A1
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shift-pol=1
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# Store pin & its active edge
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store-pin=A0
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store-pol=1
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# Clear pin & its active level
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clear-pin=A2
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clear-pol=0
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# Data port and pins
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data-port=A
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data-pins=3
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\end{inicode}
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\subsection{SIPO Commands}
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The WRITE and CLEAR\_DIRECT commands are the only ones normally used. The others provide manual control over all the output signals for debugging or testing.
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\begin{cmdlist}
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0 & \cname{WRITE}
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Load the shift registers and leave the \textit{Data} outputs in the ``trailing data'' state before sending a \textit{Store} pulse.
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&
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\begin{cmdreq}
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\cfield{u16} trailing data (packed pins)
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\item For each output (same size)
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\begin{pldlist}
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\cfield{u8[]} data to load
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\end{pldlist}
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\end{cmdreq}
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\\
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1 & \cname{DIRECT\_DATA}
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Directly write to the \textit{Data} pin(s)
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&
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\begin{cmdreq}
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\cfield{u16} values to write (packed pins)
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\end{cmdreq} \\
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2 &
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\cname{DIRECT\_CLEAR}
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Pulse the \textit{Clear} pin & \\
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3 &
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\cname{DIRECT\_SHIFT}
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Pulse the \textit{Shift} pin & \\
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4 &
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\cname{DIRECT\_STORE}
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Pulse the \textit{Store} pin & \\
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\end{cmdlist}
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