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72 lines
2.9 KiB
Text
72 lines
2.9 KiB
Text
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* PCF857x-compatible I/O expanders
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The PCF857x-compatible chips have "quasi-bidirectional" I/O lines that can be
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driven high by a pull-up current source or driven low to ground. This combines
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the direction and output level into a single bit per line, which can't be read
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back. We can't actually know at initialization time whether a line is configured
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(a) as output and driving the signal low/high, or (b) as input and reporting a
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low/high value, without knowing the last value written since the chip came out
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of reset (if any). The only reliable solution for setting up line direction is
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thus to do it explicitly.
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Required Properties:
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- compatible: should be one of the following.
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- "maxim,max7328": For the Maxim MAX7378
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- "maxim,max7329": For the Maxim MAX7329
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- "nxp,pca8574": For the NXP PCA8574
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- "nxp,pca8575": For the NXP PCA8575
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- "nxp,pca9670": For the NXP PCA9670
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- "nxp,pca9671": For the NXP PCA9671
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- "nxp,pca9672": For the NXP PCA9672
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- "nxp,pca9673": For the NXP PCA9673
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- "nxp,pca9674": For the NXP PCA9674
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- "nxp,pca9675": For the NXP PCA9675
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- "nxp,pcf8574": For the NXP PCF8574
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- "nxp,pcf8574a": For the NXP PCF8574A
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- "nxp,pcf8575": For the NXP PCF8575
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- "ti,tca9554": For the TI TCA9554
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- reg: I2C slave address.
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- gpio-controller: Marks the device node as a gpio controller.
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- #gpio-cells: Should be 2. The first cell is the GPIO number and the second
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cell specifies GPIO flags, as defined in <dt-bindings/gpio/gpio.h>. Only the
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GPIO_ACTIVE_HIGH and GPIO_ACTIVE_LOW flags are supported.
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Optional Properties:
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- lines-initial-states: Bitmask that specifies the initial state of each
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line. When a bit is set to zero, the corresponding line will be initialized to
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the input (pulled-up) state. When the bit is set to one, the line will be
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initialized the low-level output state. If the property is not specified
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all lines will be initialized to the input state.
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The I/O expander can detect input state changes, and thus optionally act as
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an interrupt controller. When the expander interrupt line is connected all the
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following properties must be set. For more information please see the
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interrupt controller device tree bindings documentation available at
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Documentation/devicetree/bindings/interrupt-controller/interrupts.txt.
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- interrupt-controller: Identifies the node as an interrupt controller.
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- #interrupt-cells: Number of cells to encode an interrupt source, shall be 2.
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- interrupt-parent: phandle of the parent interrupt controller.
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- interrupts: Interrupt specifier for the controllers interrupt.
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Please refer to gpio.txt in this directory for details of the common GPIO
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bindings used by client devices.
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Example: PCF8575 I/O expander node
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pcf8575: gpio@20 {
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compatible = "nxp,pcf8575";
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reg = <0x20>;
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interrupt-parent = <&irqpin2>;
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interrupts = <3 0>;
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gpio-controller;
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#gpio-cells = <2>;
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interrupt-controller;
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#interrupt-cells = <2>;
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};
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