Driver for character LCD module on parallel interface requiring only single I/O

Peter Jakacki

Here is a driver using a single I/O pin to drive a parallel interface LCD module. Can't be done?

Well, we are cheating a bit and reusing the I2C bus pins and plus we need a 50 cent shift register but other than that we only need a single I/O pin.
If you happen to have 1 or 2 other pins then you can use that to control the contrast and the backlight.

*Peter*

virtuPIC

Now that's what I really call 'cheating'! You need the triple amount of pins: three instead of one. For a single pin you can buy a SN74LV8153 for $1.50 which is an auto-baud deserializer up to 24 kbit/s. Funny: Price is inverse proprtional to number of pins.

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Airspace V - international hangar flying!
www.airspace-v.com/ggadgets for tools & toys

Peter Jakacki

Well, I don't know of any Prop systems that doesn't use an EEPROM and then use the I2C for something totally different so the LCD uses 3 pins but only 1 spare I/O is required.

Thanks for the heads up on the 8153, that is a nice chip and the price is good too. The autobaud is a bit of a cheat as anybody can autobaud if you are always guaranteed a fixed width low pulse which is what they require for the transmission format. But I give you that it is really neat. It's a pity they have adopted standard CMOS input levels though which means you can't drive them directly from the Prop if the 8153 runs on +5V. Cross that out! It's got a separate VCC for the outputs that go up to 12, wow!. I'm going to design these chips into my boards from now on because they only need one pin and they are cheap and they can run at 12V. Max data rate is a bit on the pedestrian side though at 24Kbps but that's ok.

You made my day.

*Peter*

Ken Peterson

This chip might be useful for page-addressing a static RAM.

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·"I have always wished that my computer would be as easy to use as my telephone.· My wish has come true.· I no longer know how to use my telephone."

- Bjarne Stroustrup

virtuPIC

Peter Jakacki said...
It's a pity they have adopted standard CMOS input levels though which means you can't drive them directly from the Prop if the 8153 runs on +5V.

Ahem... according to the TI datasheet it has outputs that you can switch between OC and push-pull on a separate power supply of up to 12 V while the inputs are run at 3 V. I consider that you can use it as an integrated voltage converter.

Okay, you have a 'data efficiency' of only 50% because each byte contains only 4 data bits. But you can drive up to eight of these chips on a single pin giving you 64 outputs!

Just in case the '8153 is too expensive you can also take a 14 pin PIC controller and emulate the 8153...

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Airspace V - international hangar flying!
www.airspace-v.com/ggadgets for tools & toys

Peter Jakacki

Well the 8153 would take around 1ms at best to update 8-bits which would be way too slow for RAM paging I would think. As to the "emulation" by a PIC I like to see a PIC that costs less and connects directly to +12V loads! PIC smoke!
The 8153 really is cheaper than I2C I/O and for around a buck the only other thing cheaper would be a plain old shift register.

*Peter*

Ken Peterson

Peter: I think you're right about it being too slow for paging RAM. Perhaps a synchronous shift register (74LV595 for example) would work better for that. Something you can clock at several MHz. Only a buck at Digikey.

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·"I have always wished that my computer would be as easy to use as my telephone.· My wish has come true.· I no longer know how to use my telephone."

- Bjarne Stroustrup

Post Edited (Ken Peterson) : 2/28/2009 7:27:03 PM GMT