NHD-C0220BA-FSW-FTW 4-bit DL

Updating a working design that used the NHD-C0220AZ-FSW-FTW and NT7605 controller to use the NHD-C0220BA-FSW-FTW and ST7036 controller. I did see a post about the contrast voltage being wrong, so will try that while waiting for a forum response. UPDATE 1: replaced the voltage divider for V0 with a potentiometer, no change to display regardless of voltage--see UPDATE 3.

The ST7036 documentation states in 4-bit mode that DB0 through DB3 are not used during 4-bit operation and must connect to VDD. The NT7605 documentation did not specify their state and the original design connected them to VSS, which worked for the NT7605. Is the ST7036 documentation correct, or does it matter? UPDATE 2: It does not appear to make a difference, unless it ends up being a current sink.

The sample code in both the ST7036 and NHD-C0220BA-FSW-FTW documentation as well as the sample Arduino code on the website include instructions to access extended instruction set functions that are not enabled on the ST7036. This is somewhat confusing.

UPDATE 3: The updated design is now working. Confusion is probably arising from NHD-C0220BA-FSW-FTW documentation copying the NHD-C0220AZ-FSW-FTW documentation. The command table does not list instruction table bits IS1 and IS0, so the 0x39 (0x29 in 4-bit mode) command in the example code is unclear what it is doing. However, it is selecting extension table 1 so that the subsequent commands turn on the power to the display and amplification bias for the liquid crystal voltage, which needs about 0.9 * VDD at V0 to appear visible.