update readme.md (#58)

- sync last commits
- update readme.md

Author: RobTillaart

CHANGELOG.md

@@ -6,14 +6,18 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/)
 and this project adheres to [Semantic Versioning](http://semver.org/).
 
 
+## [0.4.2] - 2025-04-18
+- sync last commits
+- update readme.md
+
+
 ## [0.4.1] - 2023-09-23
 - Update readme with advanced interrupts insights
   - kudos to ddowling for testing.
   - add example
 - fix URL examples
 - add Wire1 example (ESP32 + RP2040)
 
-
 ## [0.4.0] - 2023-09-23
 - refactor API, begin()
 - update readme.md
@@ -39,7 +43,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 ## [0.3.6] - 2022-10-19
 - fix example PCF8574_rotaryEncoder.ino
 - add RP2040 to build-CI
-- simplified changelog.md 
+- simplified changelog.md
 
 ## [0.3.5] - 2022-06-17
 - add select(), selectN(), selectNone() and selectAll()
@@ -49,7 +53,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 - add CHANGELOG.md
 - fix **begin(int sda, int scl)** int parameters for ESP alike.
 
-## [0.3.3] - 2021-12-23  
+## [0.3.3] - 2021-12-23
 - update library.json, license, readme, minor edits
 
 ## [0.3.2] - 2021-07-04
@@ -91,7 +95,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 - Fix/refactor ButtonRead8() - see https://github.com/RobTillaart/Arduino/issues/38
 - missing begin() => mask parameter
 
-## [0.1.07] - 2016-05-02  
+## [0.1.07] - 2016-05-02
 - (manually merged) Septillion
 - added dataOut so a write() doesn't read first,
    possibly corrupting a input pin;

LICENSE

@@ -1,6 +1,6 @@
 MIT License
 
-Copyright (c) 2013-2024 Rob Tillaart
+Copyright (c) 2013-2025 Rob Tillaart
 
 Permission is hereby granted, free of charge, to any person obtaining a copy
 of this software and associated documentation files (the "Software"), to deal

PCF8574.cpp

@@ -2,7 +2,7 @@
 //    FILE: PCF8574.cpp
 //  AUTHOR: Rob Tillaart
 //    DATE: 02-febr-2013
-// VERSION: 0.4.1
+// VERSION: 0.4.2
 // PURPOSE: Arduino library for PCF8574 - 8 channel I2C IO expander
 //     URL: https://github.com/RobTillaart/PCF8574
 //          http://forum.arduino.cc/index.php?topic=184800

PCF8574.h

@@ -3,7 +3,7 @@
 //    FILE: PCF8574.h
 //  AUTHOR: Rob Tillaart
 //    DATE: 02-febr-2013
-// VERSION: 0.4.1
+// VERSION: 0.4.2
 // PURPOSE: Arduino library for PCF8574 - 8 channel I2C IO expander
 //     URL: https://github.com/RobTillaart/PCF8574
 //          http://forum.arduino.cc/index.php?topic=184800
@@ -13,7 +13,7 @@
 #include "Wire.h"
 
 
-#define PCF8574_LIB_VERSION         (F("0.4.1"))
+#define PCF8574_LIB_VERSION         (F("0.4.2"))
 
 #ifndef PCF8574_INITIAL_VALUE
 #define PCF8574_INITIAL_VALUE       0xFF
@@ -27,7 +27,7 @@
 class PCF8574
 {
 public:
-  explicit PCF8574(const uint8_t deviceAddress = 0x20, TwoWire *wire = &Wire);
+  PCF8574(const uint8_t deviceAddress = 0x20, TwoWire *wire = &Wire);
 
   bool    begin(uint8_t value = PCF8574_INITIAL_VALUE);
   bool    isConnected();
@@ -82,7 +82,7 @@ class PCF8574
   uint8_t _dataIn {0};
   uint8_t _dataOut {0xFF};
   uint8_t _buttonMask {0xFF};
-  
+
 
   TwoWire*  _wire;
 };

README.md

@@ -16,8 +16,6 @@ Arduino library for PCF8574 - 8 channel I2C IO expander.
 
 ## Description
 
-Related to the PCF8575 16 channel IO expander library  https://github.com/RobTillaart/PCF8575
-
 This library gives easy control over the 8 pins of a PCF8574 and PCF8574A chip.
 These chips are identical in behaviour although there are two distinct address ranges.
 
@@ -36,7 +34,7 @@ The library allows to read and write both single pins or 8 pins at once.
 Furthermore some additional functions are implemented that are playful and useful.
 
 
-#### Interrupts intro
+### Interrupts intro
 
 The PCF8574 has an interrupt output line (INT) to notify an MCU that one of the input lines has changed.
 This can be used to prevent active polling of the PCF8574, which can be more efficient.
@@ -61,7 +59,7 @@ In practice if you have faster polling than your signals changes this would not
 be a problem. E.g. tactile switches and a polling frequency > 100 Hz will work.
 
 
-#### Interrupts library
+### Interrupts library
 
 The library cannot handle the PCF8574 interrupts as it has no code for it. 
 The user should catch the interrupt in his own code to set a flag and can use 
@@ -84,7 +82,7 @@ A minimal example that shows catching missed interrupts:
 - **PCF8574_interrupt_advanced.ino**
 
 
-#### 0.4.0 Breaking change
+### 0.4.0 Breaking change
 
 Version 0.4.0 introduced a breaking change.
 You cannot set the pins in **begin()** any more.
@@ -93,23 +91,27 @@ The user has to call **Wire.begin()** and can optionally set the Wire pins
 before calling **begin()**.
 
 
-#### Related
+### Related
 
 16 bit port expanders
 
-- https://github.com/RobTillaart/MCP23017_RT
-- https://github.com/RobTillaart/MCP23S17
-- https://github.com/RobTillaart/PCF8575
+- https://github.com/RobTillaart/MCP23017_RT  I2C 16 IO lines.
+- https://github.com/RobTillaart/MCP23S17  SPI 16 IO lines.
+- https://github.com/RobTillaart/PCF8575  I2C 16 IO lines.
+- https://github.com/RobTillaart/PCA9671  I2C 16 IO lines. - successor PCF8575
 
 
 8 bit port expanders
 
-- https://github.com/RobTillaart/MCP23008
-- https://github.com/RobTillaart/MCP23S08
-- https://github.com/RobTillaart/PCF8574
+- https://github.com/RobTillaart/MCP23008  I2C 8 IO lines.
+- https://github.com/RobTillaart/MCP23S08  SPI 8 IO lines.
+- https://github.com/RobTillaart/PCF8574  I2C 8 IO lines.
+
 
+## I2C
 
-## I2C Clock
+
+### Performance
 
 Tested on UNO with **PCF8574_performance** showed that the PCF8574 still works at 500 KHz and failed at 600 KHz.
 These values are outside the specs of the datasheet so they are not recommended.
@@ -125,6 +127,24 @@ However when performance is needed you can try to overclock the chip.
 |  600000     | crash  |  crash  | 
 
 
+### I2C multiplexing
+
+Sometimes you need to control more devices than possible with the default
+address range the device provides.
+This is possible with an I2C multiplexer e.g. TCA9548 which creates up 
+to eight channels (think of it as I2C subnets) which can use the complete 
+address range of the device. 
+
+Drawback of using a multiplexer is that it takes more administration in 
+your code e.g. which device is on which channel. 
+This will slow down the access, which must be taken into account when
+deciding which devices are on which channel.
+Also note that switching between channels will slow down other devices 
+too if they are behind the multiplexer.
+
+- https://github.com/RobTillaart/TCA9548
+
+
 ## Interface
 
 ```cpp
@@ -135,7 +155,7 @@ However when performance is needed you can try to overclock the chip.
 the include of "pcf8574.h" to overrule the default value used with the **begin()** call.
 
 
-#### Constructor
+### Constructor
 
 - **PCF8574(uint8_t deviceAddress = 0x20, TwoWire \*wire = &Wire)** Constructor with optional address, default 0x20, 
 and the optional Wire interface as parameter.
@@ -147,7 +167,7 @@ so one might need to call **read8()** and/or **write8()**. Returns true if addre
 - **uint8_t getAddress()** Returns the device address.
 
 
-#### Read and Write
+### Read and Write
 
 - **uint8_t read8()** reads all 8 pins at once. This one does the actual reading.
 - **uint8_t read(uint8_t pin)** reads a single pin; pin = 0..7
@@ -159,7 +179,7 @@ value is HIGH(1) or LOW (0)
 - **uint8_t valueOut()** returns the last written data.
 
 
-#### Button
+### Button
 
 The **"button"** functions are to be used when you mix input and output on one IC.
 It does not change / affect the pins used for output by masking these.
@@ -176,7 +196,7 @@ Note this can be a subset of the pins set with **setButtonMask()** if one wants
 Background - https://github.com/RobTillaart/Arduino/issues/38
 
 
-#### Special
+### Special
 
 - **void toggle(const uint8_t pin)** toggles a single pin
 - **void toggleMask(const uint8_t mask = 0xFF)** toggles a selection of pins, 
@@ -190,7 +210,7 @@ Fills the lower lines with zero's.
 - **void reverse()** reverse the "bit pattern" of the lines, swapping pin 7 with 0, 6 with 1, 5 with 2 etc.
 
 
-#### Select
+### Select
 
 Some convenience wrappers.
 
@@ -204,7 +224,7 @@ This can typical be used to implement a VU meter.
 - **void selectAll()** sets all pins to HIGH.
 
 
-#### Miscellaneous
+### Miscellaneous
 
 - **int lastError()** returns the last error from the lib. (see .h file).
 

library.json

@@ -15,7 +15,7 @@
     "type": "git",
     "url": "https://github.com/RobTillaart/PCF8574.git"
   },
-  "version": "0.4.1",
+  "version": "0.4.2",
   "license": "MIT",
   "frameworks": "*",
   "platforms": "*",

library.properties

@@ -1,5 +1,5 @@
 name=PCF8574
-version=0.4.1
+version=0.4.2
 author=Rob Tillaart <rob.tillaart@gmail.com>
 maintainer=Rob Tillaart <rob.tillaart@gmail.com>
 sentence=Arduino library for PCF8574 - 8 channel I2C IO expander