xref: /freebsd/share/man/man4/pcf8574.4 (revision 5956d97f4b3204318ceb6aa9c77bd0bc6ea87a41)
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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