[lcd4linux] HD44780 I2C driver issue

[Laurent H. <lau...@fr...>]

Hi all

I'm currently trying to use lcd4linux on a WR703N router with OpenWRT, 
with a 20x4 HD44780 LCD equipped with an I2C interface.

Unfortunately, after several hours of struggle, I finally found that the 
I2C integrated (soldered) interface -  model YwRobot LCM1602 - is 
finally not compatible with the plain HD44780-I2C driver :-(  I got the 
same behavior as the TRAC ticket #295 described.

These LCD + interfaces are sold by many vendors (mostly Chinese etc.) 
and under several brands.

Actually, the 4 bits of data are assigned to the 4 HIGHER bits of the 
"abstracted Port", and RS, RW, and EN are assigned to the LOWER bits :-(

Here is the corresponding table between the PCF8574 output pins and the LCD

    PCF 8574         LCD
Pin  Function   Pin  Function
4      P0        4      RS
5      P1        5      RW
6      P2        6      EN
7      P3        NC (backlight ?)
9      P4        11     D4
10     P5        12     D5
11     P6        13     D6
12     P7        14     D7

 From what I read on the HD44780 wiki page, in 4 bits mode, the data 
bits are ALWAYS assigned to DB0-DB3, and it seems there is no way to 
assign them to DB4-DB7 (which in turn are always assigned to control 
signals).

Can you help ?

Thanks !