Interfacing with the Wanhao i3 LCD (1 reply)

I have a Wanhao Duplicator i3 aka Monoprice Maker Select V2.1, which uses a Melzi controller board. I have successfully installed Marlin to that board, and it functions well.

I'm replacing the Melzi board with a BIGTREETECH SKR V1.4 Turbo and rebuilding Marlin for it. I'm trying to figure out how to interface with the LCD that's built into the i3's control box. Just to emphasize, Marlin worked fine with this LCD when it was attached to the Melzi, using the LCD_FOR_MELZI setting and the Sanguinololu 1.1 pin settings. (I am a novice when it comes to 3d printers and generally electronics.)

My question is how I can configure the EXP pins on the SKR through Marlin to be able to communicate with this LCD.

A commenter on a blog once wrote that he got it to work:

For those who struggles to connect the stock wanhao i3 1.2 LCD display. I got it working by connecting the following pins:
pin 1 LCD CS –> 1.19 EXP 1
pin 2 Encoder B –> 3.25 EXP 2
pin 3 LCD Data –> 1.18 EXP 1
Pin 4 Encoder A–> 3.26 EXP 2
pin 5 LCD SCLK –> 1.20 EXP 1
pin 6 Encoder Button –> 0.28 EXP 1
pin 7 ESTOP –> I dont use that one- so did not try to find it
pin 8 Beeper –> 1.30 EXP 1
Pin 9 5v –> 5V EXP 1
pin 10 GND –> GND EXP 1

LCD pins should like this:
1 2
3 4
5 6
7 8
9 10

There are a couple of things that are impeding my understanding here: Their pin labels for the LCD don't match what's silkscreened on the Melzi. I don't know what display setting they used in their configuration file. They wire the LCD display to both EXP1 and EXP2 and I'm hoping it can be done without making some unholy wiring mess that goes to both. Finally, the pin numbering doesn't comport with what is what is silkscreened on the Melzi and the Pin 1 indicator on the box header.

Here is my own diagram of what is silkscreened and how the cable attaches between the two PCBs:

/**
 *       Melzi                      SKR
 *       _____                     _____
 *  GND |10 9 | 5V             5V |10 9 | GND
 *   A4 | 8 7 | D10/RX1      1.23 | 8 7 | 1.22 
 *   A3 | 6 5   D11/TX1  ->  1.21 | 6 5   1.20 
 *   A2 | 4 3 | D16/SCL      1.19 | 4 3 | 1.18 
 *   A1 | 2 1 | D17/SDA      0.28 | 2 1 | 1.30
 *       -----                     -----
 *                                 EXP1
 */

Note that, for instance, 5V and GND appear to be reversed.

This is what the Wanhao configuration does when you enable the LCD_FOR_MELZI:

      #define LCD_PINS_RS                     17
      #define LCD_PINS_ENABLE                 16
      #define LCD_PINS_D4                     11

      #define BOARD_ST7920_DELAY_1 DELAY_NS(0)
      #define BOARD_ST7920_DELAY_2 DELAY_NS(188)
      #define BOARD_ST7920_DELAY_3 DELAY_NS(0)

Am I able to program the SKR pins to talk to the LCD?