| Electronics > Repair |
| Winstar WG192128 LCD Replacement (6800 vs 8080 interface) |
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| Nebukad:
Hi there! I am working on a GW PST-3202 Bench Power Supply - nothing super-fance but still a decent lab power supply. I was able to fix the original issue and now the only thing left is the LCD, which has been severly damaged. It's a simple 192x128 Pixel monochrome LCD with a parallel interface. The Original Display was a Winstar WG192128A (note the Rev. A). I did quite a lot of searching, but I was only able to get the newer model WG192128C (note the Rev. C). It is exactly the same size and has the same 20pin-connector or it. However, after swapping it, I only got random stuff on the screen. After even more googleing I discovered, that apparently, the Rev. A used the Motorola 6800 interface protocal, while the Rev. C now uses the Intel 8080 protocol. This can also be seen in the pinout description (see fotos). I never got in contact with any of those protocols before. One major difference appear to be the Enable and Read/Write Pins of the 6800 protocol in contrast to the /Read and /Write Pins of the 8080. I already tried to translate those pins using some 74series logic: - I pull the /Read pin low, when Enable is present and Read/Write is high - I pull the /Write pin low, when Enable is present and Read/Write is low This has stopped random-data to get written to the display, so I don't get a random image anymore, but sadly, the image is now completely blank, so something is still not write. Could someone with a little more knowledge about those display protocols maybe step in and help me out here? Is it even possible to "convert" between these two protocols or are also the commands fundamentally different? Or does anybody know, where I could get the original WG192128A display from these days? Thanks in advance! |
| coromonadalix:
sometimes you have some surface mount component to move at some places to change the working mode ... of if they are excactly the same models on the glass surface i would do a lcd change if the original board is still intact ?? show us some photos |
| srb1954:
--- Quote from: Nebukad on May 13, 2021, 08:04:39 am ---After even more googleing I discovered, that apparently, the Rev. A used the Motorola 6800 interface protocal, while the Rev. C now uses the Intel 8080 protocol. This can also be seen in the pinout description (see fotos). I never got in contact with any of those protocols before. One major difference appear to be the Enable and Read/Write Pins of the 6800 protocol in contrast to the /Read and /Write Pins of the 8080. I already tried to translate those pins using some 74series logic: - I pull the /Read pin low, when Enable is present and Read/Write is high - I pull the /Write pin low, when Enable is present and Read/Write is low Could someone with a little more knowledge about those display protocols maybe step in and help me out here? Is it even possible to "convert" between these two protocols or are also the commands fundamentally different? --- End quote --- The 6800 transfers data when the Enable signal is high while the direction of transfer is determined by the R/W signal. It is relatively straight forward to translate these 6800 bus interface signals to suit 8080 style peripherals using the RD/ and WR/ strobes. The easiest way is to use a decoder e.g. 1/2 of 74HC139 with the Enable and R/W signals taken to the A1 and A0 decoder address lines respectively. With the decoder enable input tied low the required RD/ and WR/ signals appear on the decoded Y3/ and Y2/ outputs respectively. Your decoding with the 74 series logic should have also worked - draw up a truth table for your logic and verify it generates the correct states. Also check the circuit operation with a scope as glitches in the decoding may cause spurious transfers to take place corrupting the data in the LCD controller. |
| JoeyG:
See if you can get the Winstar data sheet , it might point to the LCD controller on board, then google the controller for the data sheet and you see if it has a 8080 AND 6800 interface |
| Nebukad:
Hey guys and thanks a bunch for the replies! I've attached a photo of the old display assembly. Regarding Jumpers: There are a couple of them, but from what I figured out so far, they are purely for connecting the backlight to different signales, maybe to the logic supply or the external supply. They are set the same way on the new assembly. The two versions use different ICs (Old: LC7981, New: RA6963) and the IO pins go straight into those controllers. I'm afraid, each controller only has the one protocol, so there is nothing to change there. This also matches the rare information I found about those displays online. For the -A it says only 6800 and for the -C only 8080. Regarding swapping the LCD itself: This is indeed an option, but only my last option. Here's why: Since the LCD has no controller on it, all 192 columns and all 128 rows are individually connected to the controller PCB. the colums via 2 gigantic zebra-strips but the 128 rows via a heat-bar attachmacht. I would have to safely remove the heat-bar-attached flat-flex from the new assembly and somehow reattach it to the old controller pcb. There is no extra length to cut it. I might try it in the end, but I don't suspect, it will work. Regarding my logic: I've used a quad-Nand (74HC132), since I had that lying aroung in a breadboard-friendly DIP-package. My logic looks something like this: /RD = Enable NAND (Read/Write) /WR = Enable NAND ( Read/Write NAND Read/Write) = Enable NAND (NOT Read/Write) Looking at the circuit with a scope, I can see the following things: - There is a lot of activity on the Read/Write-Pin, even when the Enable is low. So I suspect, this bus i used for other things as well. This could explain, why there was so much crap before beeing written to the LCD. - The Enable Signal does not appear to be periodic at all. I read somewhere, that 6800 would be a synchronous interface, but this does not seem to be the case here. - Whenever the Enable signal is high, the Read/Write Signal is low. This would indicate, the the Master is never reading from the LCD but only writing to it. Which makes sense, I guess. - My circuit seems to do the write thing: Whenever the Enable Signal is high, the /WR signal is pulled low (since Read/Write is low) and /RD always stays high. But as I said: This prevents "crap" data to be written to the LCD, but now it stays completely blank. |
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