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.Dd November 6, 2021 28.Dt PCF8574 4 29.Os 30.Sh NAME 31.Nm pcf8574 32.Nd driver for the PCF8574 8-bit I2C IO expander 33.Sh SYNOPSIS 34To compile this driver into the kernel, 35place the following lines in your 36kernel configuration file: 37.Bd -ragged -offset indent 38.Cd "device pcf8574" 39.Cd "device gpio" 40.Cd "device iicbus" 41.Ed 42.Pp 43Alternatively, to load the driver as a 44module at boot time, place the following line in 45.Xr loader.conf 5 : 46.Bd -literal -offset indent 47pcf8574_load="YES" 48.Ed 49.Sh DESCRIPTION 50The 51.Nm 52driver provides 53.Xr gpiobus 4 54control over 8 GPIO pins. 55The pins are quasi-bidirectional. 56Only low output can be actively driven. 57High output is equivalent to input. 58.Pp 59On an 60.Xr FDT 4 61based system the following properties must be set: 62.Bl -tag -width "compatible" 63.It Va compatible 64Must be set to "nxp,pcf8574". 65.It Va reg 66The I2C address of 67.Nm . 68.El 69.Pp 70The DTS part for a 71.Nm 72device usually looks like: 73.Bd -literal 74/ { 75 76 ... 77 pcf8574@27 { 78 compatible = "nxp,pcf8574"; 79 reg = <0x27>; 80 }; 81}; 82.Ed 83.Sh SEE ALSO 84.Xr fdt 4 , 85.Xr gpiobus 4 , 86.Xr iicbus 4 87.Sh HISTORY 88The 89.Nm 90driver and this manual page was written by 91.An Andriy Gapon Aq Mt avg@FreeBSD.org . 92.Sh BUGS 93The 94.Nm 95driver does not support the input change interrupt 96that the hardware provides. 97