Messages in this thread | | | From | David Reaver <> | Subject | Re: [PATCH v2] auxdisplay: hd44780: move cursor home after clear display command | Date | Wed, 26 Jul 2023 08:12:41 -0700 |
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Hugo Villeneuve <hugo@hugovil.com> writes:
> From: Hugo Villeneuve <hvilleneuve@dimonoff.com> > > The DISPLAY_CLEAR command on the NewHaven NHD-0220DZW-AG5 display > does NOT change the DDRAM address to 00h (home position) like the > standard Hitachi HD44780 controller. As a consequence, the starting > position of the initial string LCD_INIT_TEXT is not guaranteed to be > at 0,0 depending on where the cursor was before the DISPLAY_CLEAR > command. > > Extract of DISPLAY_CLEAR command from datasheets of: > > Hitachi HD44780: > ... It then sets DDRAM address 0 into the address counter... > > NewHaven NHD-0220DZW-AG5 datasheet: > ... This instruction does not change the DDRAM Address > > Move the cursor home after sending DISPLAY_CLEAR command to support > non-standard LCDs. > > Signed-off-by: Hugo Villeneuve <hvilleneuve@dimonoff.com> > --- > drivers/auxdisplay/hd44780_common.c | 10 +++++++++- > 1 file changed, 9 insertions(+), 1 deletion(-) > > diff --git a/drivers/auxdisplay/hd44780_common.c b/drivers/auxdisplay/hd44780_common.c > index 3934c2eebf33..7cbf375b0fa5 100644 > --- a/drivers/auxdisplay/hd44780_common.c > +++ b/drivers/auxdisplay/hd44780_common.c > @@ -82,7 +82,15 @@ int hd44780_common_clear_display(struct charlcd *lcd) > hdc->write_cmd(hdc, LCD_CMD_DISPLAY_CLEAR); > /* datasheet says to wait 1,64 milliseconds */ > long_sleep(2); > - return 0; > + > + /* > + * The Hitachi HD44780 controller (and compatible ones) reset the DDRAM > + * address when executing the DISPLAY_CLEAR command, thus the > + * following call is not required. However, other controllers do not > + * (e.g. NewHaven NHD-0220DZW-AG5), thus move the cursor to home > + * unconditionally to support both. > + */ > + return hd44780_common_home(lcd); > } > EXPORT_SYMBOL_GPL(hd44780_common_clear_display); > > > base-commit: d192f5382581d972c4ae1b4d72e0b59b34cadeb9
I tested this on a 16x2 HD44780 on my BeagleBone Black with:
$ printf '\f' > /dev/lcd $ printf 'Hello\nWorld!\n' > /dev/lcd $ printf '\x1b[LR' > /dev/lcd $ printf '\x1b[LR' > /dev/lcd $ printf '\x1b[LR' > /dev/lcd $ printf '\f' > /dev/lcd $ printf 'Goodbye\nWorld!\n' > /dev/lcd
As expected, "Goodbye World!" was correctly placed left-aligned on the display, split over both lines.
Tested-by: David Reaver <me@davidreaver.com>
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