1.\" 2.\" SPDX-License-Identifier: BSD-2-Clause 3.\" 4.\" Copyright (c) 2020 Andriy Gapon <avg@FreeBSD.org> 5.\" 6.\" Redistribution and use in source and binary forms, with or without 7.\" modification, are permitted provided that the following conditions 8.\" are met: 9.\" 1. Redistributions of source code must retain the above copyright 10.\" notice, this list of conditions and the following disclaimer. 11.\" 2. Redistributions in binary form must reproduce the above copyright 12.\" notice, this list of conditions and the following disclaimer in the 13.\" documentation and/or other materials provided with the distribution. 14.\" 15.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 16.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 17.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 18.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 19.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 20.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 21.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 22.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 23.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 24.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 25.\" SUCH DAMAGE. 26.\" 27.\" $FreeBSD$ 28.\" 29.Dd November 6, 2021 30.Dt PCF8574 4 31.Os 32.Sh NAME 33.Nm pcf8574 34.Nd driver for the PCF8574 8-bit I2C IO expander 35.Sh SYNOPSIS 36To compile this driver into the kernel, 37place the following lines in your 38kernel configuration file: 39.Bd -ragged -offset indent 40.Cd "device pcf8574" 41.Cd "device gpio" 42.Cd "device iicbus" 43.Ed 44.Pp 45Alternatively, to load the driver as a 46module at boot time, place the following line in 47.Xr loader.conf 5 : 48.Bd -literal -offset indent 49pcf8574_load="YES" 50.Ed 51.Sh DESCRIPTION 52The 53.Nm 54driver provides 55.Xr gpiobus 4 56control over 8 GPIO pins. 57The pins are quasi-bidirectional. 58Only low output can be actively driven. 59High output is equivalent to input. 60.Pp 61On an 62.Xr FDT 4 63based system the following properties must be set: 64.Bl -tag -width "compatible" 65.It Va compatible 66Must be set to "nxp,pcf8574". 67.It Va reg 68The I2C address of 69.Nm . 70.El 71.Pp 72The DTS part for a 73.Nm 74device usually looks like: 75.Bd -literal 76/ { 77 78 ... 79 pcf8574@27 { 80 compatible = "nxp,pcf8574"; 81 reg = <0x27>; 82 }; 83}; 84.Ed 85.Sh SEE ALSO 86.Xr fdt 4 , 87.Xr gpiobus 4 , 88.Xr iicbus 4 89.Sh HISTORY 90The 91.Nm 92driver and this manual page was written by 93.An Andriy Gapon Aq Mt avg@FreeBSD.org . 94.Sh BUGS 95The 96.Nm 97driver does not support the input change interrupt 98that the hardware provides. 99