Driving a little LCD

Does it really have to be fully static? Why not, say, a triplexed display?

Best regards, Spehro Pefhany

I was simply going with what I initially found.

If you have some specific ideas, I'm all ears. I'm new to driving LCDs.

Graham

Microchip sells a bunch of PIC microcontrollers which are designed specifically to drive LCDs. Ferexample, their PIC16F913 is a 28-pin part which can drive certain LCD configurations having up to 60 addressable segments.

I believe that other micro vendors have similar parts in their stables.

You might be able to use an LCD-capable micro of this sort as your primary programmable device... or, use one as a display-management peripheral, talking to your main micro over a UART or other serial interface.

Do you know how they do that ? Presumably there's an app note ?

Ideally I'd like to stick with a member of the 8051 family for familiarity.

Yes, the thought had crossed my mind although I doubt that would be brilliant for cost.

Graham

No doubt - they're quite good about providing howto-doit notes.

I would guess that the LCDs in question are generally multiplexed in a matrixed arrangement, with some fraction being anodes and the rest cathodes.

Philips (now NXP) has always been big in the 8051 architecture. It looks as if the P89LPC94x family might do what you want - it's an 8051 derivative and a "universal LCD controller" integrated into a 64-pin multi-chip module. Toughest part may be trying to get samples, if what I hear about NXP is true.

I found some info. It's quite intruiging how the multiplexing works. Not as simple as with LEDS or VFDs by a long shot !

Thanks, I'll check that one out.

TI has one of the MSP430s that could be purpose made for this app too. Shame I'm not familiar with them.

Graham

I'm

Get familiar, free up your brain from juggling with memory spaces and pointer snafus. UARTs and timers are much nicer too. MSPGCC works well, and doesn't cost a lot, and C will (may?) make porting easier (even if you've written your app in assembler). The BIG downside is it's 3.6V max and no 5V compliant IO.

Paul Burke

Buy this serial LCD display, BPI-216, from:

It save you a LOT of trouble. I'm using one now.

Al

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If you use a micro with an on-board controller, you just need to match the driver to the chip and set it up properly. There's a chunk of RAM and you just deposit a bitmap of the desired display pattern. There are flash chips available from TI, Freescale, Microchip and others that will handle displays with multiple backplanes. Offhand I don't recall which 8051 variants have this ability, but I'm sure there are some by now. As the number of backplanes (and the mux ratio) increases, you save pins for the segment drive, but the on/off characteristics suffer (for example, the contrast may be poor, vary from unit-to-unit, shift substantially with temperature or the viewing angle may not be as good as you would like). A triplexed display is almost as good as a static with n/3 + 3 pins used rather than n + 1 pins (for n segments) (if the resistor chain isn't on-chip there might be a couple more pins used).

It's also possible to use an ordinary micro eg. 89S52 to drive even a muxed display but it uses a whack of passives and would only be appropriate where volumes are large and assembly costs small.

A 28-pin PIC16F913 is a comparable chip to many 8051 variants, and can directly drive up to 60 LCD segments, for GBP ~95p in 1K, but feel free to spend a few days searching for the ideal part. It's probably out there somewhere.

Best regards, Spehro Pefhany

"Al" schrieb im Newsbeitrag news: snipped-for-privacy@news.verizon.net... | Buy this serial LCD display, BPI-216, from: | |

I can't believe it. There are guys who buy it for that price? I can sell you serial LCD 2x40 for $15 with EL backlight.

- Henry

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I'm

The PL/M compiler means I never have to consider them anyway.

MSPGCC ?

Why would anyone even use assembler these days for this kind of thing ?

Graham

Do they still make the 8748? As far as I remember, it was like an

Or, shop around for one with a built-in controller - that's probably what I'd do in this case.

Good Luck! Rich

Sorry, the 8748 is the 8048 with a built-in EPROM. Its CPU core is

driving

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Just as a 'first off' that I can easily get from Farnell I'm looking at the VI-402 from Trident Microsytems. I'm sure it'll be a widely '2nd sourced' part. In fact I'm sure Trident will just buy it in to distribute.

Graham

VI-402

fact I'm

--- Hmm... Farnell rejects that part number. Are you sure it isn't a VI-402 from Varitronix LTD?

In any case, no matter who's display it is, if you want to use the National part it'll work because you won't need the decimal points. That is, unless you want to display temperature in degrees and tenths of a degree, and then you'll only need DP3, so worst case would be 28 segments for the digits and the colon, so you'd only need to drive 29 pins.

Incidentally, segment 'f' of digit 1 is never used either (unless you want to arrange your display to display temp on the two left digits, then leave a space, and then display 'C' on the fourth digit and the temp goes above 40C) so you could connect it to the backplane with all the other unused stuff and get by with 28 segments like this Intersil part has available:

-- JF

VI-402

fact I'm

VI-402

fact I'm

Same beast.

Very true. I'd like to keep the colon and 1 decimal point so that saves 2 connections.

Neat thinking !

Graham