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4bit vs 8bit pinout for 6963 LCD
Old 5th December 2019
  #1
Gear Head
 

4bit vs 8bit pinout for 6963 LCD

I'm trying to put a 240x60 6963 style LED screen into a device that uses a 12 pin, 4bit protocol instead of the usual 22 pin, 8 bit situation.

I'm having trouble matching the terminology/concepts from the 4 bit schematic with the LCD datasheet, which I think assumes 8 bit operation.

On the 8bit side I have pins with names like Write Signal, Read signal, Chip Enable , C/D (H:instruction, L:data), and Reset Signal Input, but the 12 pin schematic shows an entirely different set of terms like Latch Pulse, Y Driver, Wire Frame, and XSCL.

Do these sets of terms match up in any way? Been trying all kinds of combinations, but I can't quite figure it out.
Old 5th December 2019
  #2
Lives for gear
 
Radardoug's Avatar
 

Study the data sheets, but they look totally incompatible to me. The 4 line model may be some form of serial bus.
Old 5th December 2019
  #3
Gear Head
 

Yeah, I'm starting to think that they are not compatible. There is apparently some way to rig a 6963 in 4 bit mode, but the LCD unit probably needs special hardware.

Leaning towards trying to revive the existing screen. It's a RM1X with fading letters on the LCD that are still visible at an extreme angle and contrast setting. The weird thing is, I have 2 RM1X screens, and they both show the same uniform fading when tested on the PCB. One of them has lines in the graphic that implies bad connection with the cable, but the fading itself seems to be uniform across both screens. I've heard of heat+pressure to re-establish contact on the LCD panel, but I feel like that issue would show a more splotchy fading.

Any thoughts?
Old 6th December 2019
  #4
Gear Head
 

Seems like the fading problem is the LCD panel deteriorating after all. Leaving the unit powered on for a good while heated the screen up, and just that has been enough to make it usably legible.
Old 6th December 2019
  #5
Lives for gear
 

The 8 bit one sounds like a controller interface (as in something that gets sent commands to draw characters or lines or scroll or whatever), while the other may be more a raw interface where you give a pixel clock and sync pulses and individual pixel values, refreshed many times a second, very much like a standard raster video signal.

Standard four bit LCD interfaces, at least the ones with a controller that I've come across, are very similar to the 8 bit interface but have four rather than eight data lines and require twice as many bus cycles to do anything. Many (most? practically all?) controller chips will work in either mode, and so adapting an eight bit interface to a four bit device just means making a cable with the appropriate connections, leaving the upper bits disconnected. If memory serves, one of the initialization steps for the eight bit interface is to give a command to shift into eight bit mode so it uses those additional data lines....
Old 6th December 2019
  #6
Gear Head
 

Yeah, the 8 bit one even has a pin for Font Selection, while the 4 bit is has a XY grid of some sort.

I did try leaving the first 4 data pins empty and matching other pins as best as I could, but it didn't really get anywhere. (Leaving just the negative voltage pin out made some cool graphics that would move with the contrast knob, but yeah...) It sounds like 6963s operate at 8 bit by default, and require an initialization sequence to go into 4bit.

I've also noticed other LCDs on the market often specify 4 or 8bit operation, with a few being able to do both. My LCD doesn't mention the subject, but it's clearly operating at 8bits. I might write them and ask
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