Date: Fri, 22 Oct 2021 11:25:32 +0300 From: Andriy Gapon <avg@FreeBSD.org> To: Olivier <Olivier.Nicole@cs.ait.ac.th>, freebsd-arm@freebsd.org Subject: Re: Using 20x4 LCD display Message-ID: <2c56fffe-327b-dd56-fa08-bc013a8881cd@FreeBSD.org> In-Reply-To: <wu7o87h1rhk.fsf@banyan.cs.ait.ac.th> References: <wu7o87h1rhk.fsf@banyan.cs.ait.ac.th>
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On 22/10/2021 09:52, Olivier wrote: > Hello, > > I would like to use a 20x4 LCD display attached to a Raspberry Pi > running FreeBSd 12.2. > > I can talk to the display through the I2C interface, when I send > something the back light will turn off and on, so the link is > established. > > What I cannot find is the sequence of codes to send in order to write a > character on te screen, to move the cursor around, etc. > > All documentation I could find so far relate to Raspbian or Arduino and > are always using high level libraries (I could not find such on FreeBSD, > equivalent to WiringPi). > > Whatever random characters I send to the screen, it persistently shows > alternating empty lines and lines or black boxes. > > Any help pointing me in the right direction will be greatly appreciated. I have a small utility for talking to a character LCD display via gpio. I am not sure about your exact hardware, but typically the I2C interface is just a GPIO-over-I2C (aka an I2C I/O expander). The utility is here: https://github.com/avg-I/gpiolcd It's based on ppilcd utility written for driving such LCDs connected to a parallel port. That utility can be found at share/examples/ppi/ppilcd.c. It uses parallel port ioctl-s for the job. To use my utility you need the LCD to be presented as a gpio device. For that you need a driver for a specific I2C to I/O port expander that you have. In my case it's PCF8574. You can search the internet for information about how HD44780 (and similar) works. https://www.exploreembedded.com/wiki/LCD_16_x_2_Basics http://web.alfredstate.edu/faculty/weimandn/lcd/lcd_addressing/lcd_addressing_index.html https://www.ti.com/product/PCF8574 P.S. In case you also have PCF8574 or compatible, I have a driver for it but I haven't committed it yet. You can find it here: https://github.com/avg-I/freebsd/commit/fb31fe9a933d62c7af96b0ab830b98cbfeed5309 -- Andriy Gapon
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