How it works: The PFC8574T I2C 8 Bit Adapter with the Vishay 20x4 LCD
Using the I2C 4 line LCD https://www.rhydolabz.com/wiki/?p=16424 There is a section on the I2C LCD Backpack. The PFC8574T I2C to 8 bit IO adapter backpack onto Vishay LCD-020N004L PFD8574 -------------------> 20x4 LCD Header Strip (4) D0 4 Rs H/L Register Select (5) D1 5 R/W H/L Read/write (6) D2 6 E H/L Enable (7) D3 --NC-- (9) D4 11 DB4 data bus 0x10 (10) D5 12 DB5 data bus 0x20 (11) D6 13 DB6 data bus 0x40 (12) D7 14 DB7 data bus 0x80 only the upper 4 bits are used to write a character into the LCD, the lower 3 bits are control bits. PFC8574 DataSheet https://www.nxp.com/docs/en/data-sheet/PCF8574_PCF8574A.pdf https://www.ti.com/lit/ds/symlink/pcf8574.pdf?ts=1588173075877 http://raspberry-at-home.com/lcd-for-