RE LCD Display - Page 1
Forum section: electronics / general

author: metrologist
author_rank: Super Contributor
timestamp: April 12, 2022, 05:35:48 pm
content: I've acquired a MODEL DE/280A Digital Electronics Corp display. These are out there but I have not found a communication protocol or pinout. I think mine is a little newer than the pictures here but same chips and labeling. That main chip, DE280A, is there any hope of figuring it out?

author: metrologist
author_rank: Super Contributor
timestamp: April 12, 2022, 06:00:10 pm
content: I found some info:https://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=1091816The DE/280A accepts ASCII signals forthe normal upper and lower case 96-character set and also for the expandedset, which, includes Katakana andselected ECMA characters. An on-boardmicroprocessor handles decoding,character generation, display buffering,cu,rsor control, auto flashing of any orall characters, refresh, programmablereset, self-test, and a blinking visible orinvisible cursor. All drive electronicsare included along with necessarypower conversion circuitry to adaptincoming +5 Vdc to tube voltages.Jumper selectable Bd rates (1200,2400,and 4800) are available for serial interfacing. Parallel interface is also standard. RS-232 voltage levels are optional. All character positions arerandomly addressable. One additionalfeature of the DE/280A is that it is thesame form, fit, and function as DECO'ssingle-line 40-character module, theDE/245A. Consequently, either displaycan be used in a design without anychanges in dimensions or user software.

author: DavidAlfa
author_rank: Super Contributor
timestamp: April 13, 2022, 12:39:20 am
content: You could try reading the rom from the P8042AH.Check thedatasheet, the verification sequence is explained, although it's a bit scary

author: metrologist
author_rank: Super Contributor
timestamp: April 13, 2022, 01:44:26 pm
content: That seems like the smart way to start. I wasn't even smart enough to recognize the chip number but at least the datasheet gives me some ideas of where to look for data pins, where my approach would be to inject some random serial data, or think I've found the parallel data pins and load up the LiquidCrystal Arduino library and... of course that would never get anywhere, no chicken dinner.I remember a video that Dave did on these vacuum displays though, and he figured out the data protocol. Wouldn't that be amazing if it was the same product? Unlikely, but I'll go look for his video. Otherwise, these are around the market and it seems a protocol could be found. I haven't found it.

author: metrologist
author_rank: Super Contributor
timestamp: April 13, 2022, 02:07:03 pm
content: Ah yes, here we go...maybe there is hope. At least I can still remember that I saw this seven years ago...

author: metrologist
author_rank: Super Contributor
timestamp: April 14, 2022, 06:13:22 am
content: The pinout is basically the same as with Dave's, just a different layout.I buzzed all the pins to the P8042 chip and connected d0 to d7 and the remaining 5 lines to Arduino. The remaining pins were all ground.CHIP SELECT: Chip select input used to select one UPI microcomputer out of several connected to a common data bus.READ:I/O read input which enables the master CPU to read data and status words from the OUTPUT DATA BUS BUFFER or status register.COMMAND/DATA SELECT: Address Input used by the master processor to indicate whether byte transfer is data (A0=0, F1 is reset) or command (A0=1, F1 is set). A0=0 during program and verify operations.WRITE:I/O write input which enables the master CPU to write data and command words to the UPI INPUT DATA BUS BUFFER.One pin goes to a MC1489 Quad Line EIA-232D Receiver Input A to Output A and then to the P8042 FREQUENCY REFERENCE:TEST 1 (T1) also functions as the event timer input (under software control).I set the data lines to B (01000010) and tried all manner of highs/lows and pulsing the other pins. Usually the LCD boots to dim chars on each side. It looks like it's trying to refresh all of the digits way too fast. Rarely it boots to some kind of test mode where almost all characters are lit and it changes between two states, or cycles through random character sets, or a couple times populated A one-by-one until most of the characters were full, then it went off.

author: metrologist
author_rank: Super Contributor
timestamp: April 14, 2022, 06:16:49 am
content: And now I noticed my first photo is from the internet and it is missing U14, but has E3 and R5. Those connections are involved with the input pin that routes through U14 and back to the P8042 TEST port.

author: metrologist
author_rank: Super Contributor
timestamp: April 14, 2022, 02:06:05 pm
content: I discovered that the display had a ribbon cable with ground and the input to the EIT-232D receiver chip, which goes back to TEST1 pin on the slave micro. The person thought it used serial input. I can't decode what signal that pin should have. A clock signal, serial in, or just a H/L toggle. The R5 and E3 jumper looks to have been cut off, and those seem to put a pull-down in circuit and tie TEST1 to ground.

author: metrologist
author_rank: Super Contributor
timestamp: April 18, 2022, 05:07:31 pm
content: I found some Arduino programs to send serial data, so I tried sending all of the ascii characters in different formats and speeds, toggling the other pins to ground. The display has a mind of its own and I have not gotten any response.I also do not understand why MC1489 is used? The control pin is just left floating as far as I can tell and the signal seems to just pass through the chip back to pin 39 on the main control. But it looks like a NAND gate to me so I don't understand it.

author: DavidAlfa
author_rank: Super Contributor
timestamp: April 19, 2022, 10:22:20 am
content: Consider making the schematic for that connector...

author: metrologist
author_rank: Super Contributor
timestamp: April 19, 2022, 02:45:33 pm
content: I'm sorry but not sure what is wanted. The connector side is mostly direct to the P8042 chip, except one of the TEST pins, which runs through an IEC-232 xceiver chip. I can't figure out what that chip is for but the effect is that the serial data just picks up a bunch of noise. The "Control" has no connection, and output goes to TEST1 as shown in chip's block diagram below. I think the rest of the chips on the board are just serial-to-parallel data latches, but where are they getting serial input, for each of the 11 chips?I think something is defective anyway as it boots up doing different things, and at some point characters were overwriting seemingly with the clock of the serial data, then just stops and goes off.Looking at the other side of the chip there are a couple parallel busses that I guess each works a different line of the display, or maybe not. Dave mentioned that if you could not figure out the protocol of the main slave processor, then you could suck it out and work the other side.

author: PlainName
author_rank: Super Contributor
timestamp: April 19, 2022, 04:59:50 pm
content: QuoteIf it's not actual V.24 signalling it could be just to provide pin protection (+/-30V) and/or level shifting. Simpler than messing about with zeners/reistors/transistors or whateve when you don't know what some berk might try feeding into that pin.