A while ago I bought one of these generic black PCF8574 I2C LCD backpacks on ebay:
A couple of days ago I went to use it for the first time with an 18M2 chip and a 16x2 LCD.
I connected power and I got the expected line of blocks on line 1.
So I got AlleyCat's 'I2C Bus Search' program from here https://picaxeforum.co.uk/threads/picaxe-to-serial-converter.31940/post-332388
and it reported finding a chip at the PICAXE format $4E address, exactly as expected.
Then I gotHippy's I2C-LCD.txt test program from here https://picaxeforum.co.uk/threads/lcd-i2c-display-with-14m2.31934/post-331937
but when I downloaded it to my 18M2 the backlight went off and the display appeared to be blank.
A web search quickly found the following schematic and if you look at the picture of my backpack you'll see the transistor next to the LED backlight jumper.
So my PCF8574 backpack has pin P3 on the PCF8547 chip controling the LCD backlight and if pin P3 is not set high the backlight will be off.
To work with this type of backpack Hippy's code needs to have the backlight pin set to 1, like this:
Symbol bitBL = bit11
bitBL = 1
A couple of days ago I went to use it for the first time with an 18M2 chip and a 16x2 LCD.
I connected power and I got the expected line of blocks on line 1.
So I got AlleyCat's 'I2C Bus Search' program from here https://picaxeforum.co.uk/threads/picaxe-to-serial-converter.31940/post-332388
and it reported finding a chip at the PICAXE format $4E address, exactly as expected.
Then I gotHippy's I2C-LCD.txt test program from here https://picaxeforum.co.uk/threads/lcd-i2c-display-with-14m2.31934/post-331937
but when I downloaded it to my 18M2 the backlight went off and the display appeared to be blank.
A web search quickly found the following schematic and if you look at the picture of my backpack you'll see the transistor next to the LED backlight jumper.
So my PCF8574 backpack has pin P3 on the PCF8547 chip controling the LCD backlight and if pin P3 is not set high the backlight will be off.
To work with this type of backpack Hippy's code needs to have the backlight pin set to 1, like this:
Symbol bitBL = bit11
bitBL = 1