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IO_PCF8575.h
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IO_PCF8575.h
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/*
* © 2023, Paul Antoine, and Discord user @ADUBOURG
* © 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 <https://www.gnu.org/licenses/>.
*/
/*
* The PCF8575 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_PCF8575_H
#define IO_PCF8575_H
#include "IO_GPIOBase.h"
#include "FSH.h"
class PCF8575 : public GPIOBase<uint16_t> {
public:
static void create(VPIN firstVpin, uint8_t nPins, I2CAddress i2cAddress, int interruptPin=-1) {
if (checkNoOverlap(firstVpin, nPins, i2cAddress)) new PCF8575(firstVpin, nPins, i2cAddress, interruptPin);
}
private:
PCF8575(VPIN firstVpin, uint8_t nPins, I2CAddress i2cAddress, int interruptPin=-1)
: GPIOBase<uint16_t>((FSH *)F("PCF8575"), firstVpin, nPins, i2cAddress, interruptPin)
{
requestBlock.setReadParams(_I2CAddress, inputBuffer, sizeof(inputBuffer));
}
// The PCF8575 handles inputs by applying a weak pull-up when output is driven to '1'.
// The pin state is driven '1' if the pin is an input, or if it is an output set to 1.
// Unused pins are driven '0'.
void _writeGpioPort() override {
uint16_t bits = (_portOutputState | ~_portMode) & _portInUse;
I2CManager.write(_I2CAddress, 2, bits, bits>>8);
}
// The PCF8575 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 {
_writeGpioPort();
}
// 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[2];
I2CManager.read(_I2CAddress, buffer, 2);
_portInputState = (((uint16_t)buffer[1]<<8) | buffer[0]) | _portMode;
} 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 = (((uint16_t)inputBuffer[1]<<8) | inputBuffer[0]) | _portMode;
else
_portInputState = 0xffff;
}
// Set up device ports
void _setupDevice() override {
_writePortModes();
_writeGpioPort();
_writePullups();
}
uint8_t inputBuffer[2];
};
#endif