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> Startac Dot Matrix Led Driver Or Protocol, Motorola StarTac Dot matrix led protocol
w4r10
Posted: October 03, 2017 09:23 pm
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Hello, i've been saved (see attachment) this piece of hardware for a long time, hoping someone, someday, help me with the pinout so i could interface with some electronics and make it shine, any one know how? any information is apreciated.

this is a led display from a motorola startac like this:
MobileCollectors Motorola StarTac

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damien
Posted: October 03, 2017 09:50 pm
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Most likely under those black blobs is a proprietary chip specific only to that model of phone. Unlikely you'll find the pinouts and what each tab then requires.

Damien


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Sch3mat1c
Posted: October 04, 2017 10:32 am
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Ooh, full of test points. Nice.

No part numbers, and the board itself being a custom assembly for the product, you're simply not going to find info on the module itself. You have to make it up yourself! biggrin.gif

If you have any of the base set to go with, you can plug them back together and sniff the signals with an oscilloscope.

Offhand, it looks like there are 5 supply pins, one or more of which will be ground. It's not obvious why they'd need so many (or so few, to the extent that, they aren't using every other pin for VCC/GND to attain good signal quality). The remaining 6? pins might be a serial bus, or a nibble-wide parallel bus (like the HD44780 4-bit interface).

It would be quite difficult to fully reverse the interface, but possible.

The first step is determining power and ground. It may be that multiple power and ground pins are used, for increased current capacity and signal quality. Find all the groups. When you make a connection, just use a ribbon cable or header (like the footprint implies), and connect all the pins within each group together at the far end.

I would guess they would use +5V for LEDs, +3.3 or 5V for logic, and ground. There could always be more supplies for weird reasons, but you'll have to figure it out.

Anyway, second step is figuring out the relationship between the supply groups, and the signal pins. Use a diode test and write down the voltage drop for each pair, and which directions they are. Write out the equivalent circuit. Most likely, supplies will have many diodes in common, and signals will have pairs of diodes (one up from GND, one down to VDD). If there are separate supplies, they may not have diodes connecting to any other supplies; sometimes, they will (this is typical for chips with multiple supplies -- the diodes prevent one supply from being above or below the other, and enforce startup sequencing).

Since you have so many testpoints handy, you can check if rows and columns are accessible (on diode testing, an LED should light up, and you'll get ~1.5V instead of ~0.6V), and check if their drivers (there should be a row of Pch pull-ups and a column of Nch pull-downs) have a relationship (body diode) to which supply pins.

Once you've mapped out supplies and signals, you can begin attempting to talk with it. At first you might just breadboard things and poke pins to see what happens; later, you'll need better timing, and actual data, for which a microcontroller will be best. In any case, always drive a pin through a resistor, 1kohm say, in case it's not always an input, or you've got an output by mistake! By comparing the driven (your side of the resistor) and pin voltages, you can tell if a pin is ever asserted by the board, or if it's always input/output.

If it's a nibble bus, expect a couple control signals for always-input, a couple control signals for always-output or open-collector, and four data pins which will be bidirectional (sometimes, they are inputs, read when a control input is active; sometimes they are outputs, engaged when another control input is active).

Finally, you have to determine the command set. The HD44780 is probably still a good starting point. You have to figure out if it accepts commands a nibble at a time (and therefore, if you need to send a byte command, it takes two consecutive nibbles!), and you have to test all possible commands to see if it responds to anything.

Again, if it's like HD44780, it probably won't respond to much, until you've sent some initialize and reset and clear and mode setting commands. This may take a lot of guessing to figure out, but you can eventually get there.

Alternately, there's the reverse method: if you can find any possible documentation whatsoever about this board, its components, its interface, or the base unit, that might give you some clues. Or if you had a spare, you could have the chips decapped, and looking under a magnifier, see if they have any designations on them. Then you look for any information on that chip -- you may very well happen into a datasheet for the thing! Or, you can look for contemporary modules: this may've been a standard off-the-shelf product back in the day, or a variant of one, or certainly using the same chips (if not the same wired interface) as other modules used. Or even more "hail-mary" than that, you can just start looking around for old LED matrix driver ICs, and see if any look like they might've been used here! (Old info can be hard to find: stuff like this was probably OEM, so at best you might find an old catalog listing such parts, but no real data on them. Catalogs, databooks and old stuff like that is hard to find online, too. Mostly you just find the latest version of newer things. For as much data as is accessible on the internet, it doesn't have a great memory!)

Tim


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