/* * © 2021, Neil McKechnie. All rights reserved. * * This file is part of DCC++EX API * * This is free software: you can redistribute it and/or modify * it under the terms of the GNU General Public License as published by * the Free Software Foundation, either version 3 of the License, or * (at your option) any later version. * * It is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the * GNU General Public License for more details. * * You should have received a copy of the GNU General Public License * along with CommandStation. If not, see . */ /* * The PCF8574 is a simple device; it only has one register. The device * input/output mode and pullup are configured through this, and the * output state is written and the input state read through it too. * * This is accomplished by having a weak resistor in series with the output, * and a read-back of the other end of the resistor. As an output, the * pin state is set to 1 or 0, and the output voltage goes to +5V or 0V * (through the weak resistor). * * In order to use the pin as an input, the output is written as * a '1' in order to pull up the resistor. Therefore the input will be * 1 unless the pin is pulled down externally, in which case it will be 0. * * As a consequence of this approach, it is not possible to use the device for * inputs without pullups. */ #ifndef IO_PCF8574_H #define IO_PCF8574_H #include "IO_GPIOBase.h" class PCF8574 : public GPIOBase { public: static void create(VPIN firstVpin, uint8_t nPins, uint8_t I2CAddress, int interruptPin=-1) { if (checkNoOverlap(firstVpin, nPins)) new PCF8574(firstVpin, nPins, I2CAddress, interruptPin); } private: PCF8574(VPIN firstVpin, uint8_t nPins, uint8_t I2CAddress, int interruptPin=-1) : GPIOBase((FSH *)F("PCF8574"), firstVpin, min(nPins, 8), I2CAddress, interruptPin) { requestBlock.setReadParams(_I2CAddress, inputBuffer, 1); } // The pin state is '1' if the pin is an input or if it is an output set to 1. Zero otherwise. void _writeGpioPort() override { I2CManager.write(_I2CAddress, 1, _portOutputState | ~_portMode); } // The PCF8574 handles inputs by applying a weak pull-up when output is driven to '1'. // Therefore, writing '1' in _writePortModes is enough to set the module to input mode // and enable pull-up. void _writePullups() override { } // The pin state is '1' if the pin is an input or if it is an output set to 1. Zero otherwise. void _writePortModes() override { I2CManager.write(_I2CAddress, 1, _portOutputState | ~_portMode); } // In immediate mode, _readGpioPort reads the device GPIO port and updates _portInputState accordingly. // When not in immediate mode, it initiates a request using the request block and returns. // When the request completes, _processCompletion finishes the operation. void _readGpioPort(bool immediate) override { if (immediate) { uint8_t buffer[1]; I2CManager.read(_I2CAddress, buffer, 1); _portInputState = buffer[0]; } else { requestBlock.wait(); // Wait for preceding operation to complete // Issue new request to read GPIO register I2CManager.queueRequest(&requestBlock); } } // This function is invoked when an I/O operation on the requestBlock completes. void _processCompletion(uint8_t status) override { if (status == I2C_STATUS_OK) _portInputState = inputBuffer[0]; else _portInputState = 0xff; } // Set up device ports void _setupDevice() override { _writePortModes(); } uint8_t inputBuffer[1]; }; #endif