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I've seen microcontrollers which claim to drive LCD segments.

For example, the CC430 can drive 96 segments. But, it's a 64 pin chip.

So, it must be providing signals for some kind of mux, what is this interface called?

For dot matrix LCDs, could a microcontroller like this drive more than 96 segments by scanning? I want to drive a small (eg. 32x32 pixel display).

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Microcontrollers that drive LCDs are typically for driving segmented LCD with very few segments. They are typically made of custom LCD glass and how the display is multiplexed is built into the LCD glass itself. You will need to check with the display vendor to determine how many common and segment lines there are for your LCD and how they are wired. For a dot matrix LCD you will probably need an external LCD controller. The LCD display vendor can probably recommend one.

For some background in how a on-chip LCD module works.
Microchip application note AN658

EDIT: NXP Has a number of LCD segment drivers available and application notes explaining how to use them. I have not seen a microcontroller that has a built in LCD driver for more than a few segments and certainly not 1024. I'd recommend something like the PCF8576C. You can cascade multiple chips together to drive more segments.

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First, there are many types of dot matrix displays, some even receive ASCII data via parallel or serial buses, the following answer covers the pixel-addressable ones.

The dot matrix displays that I've analysed (various LED, LCD and a pair of fluorescent ones, all grey-scale) use two lines (for v-clock and h-clock) and one line for pixel value, internally they integrate a mux for one dimension and a shift-register for the other (used as a counter). Sometimes, for adding shades of gray, the MCU holds the clock for the shift-register and refreshes the same line several times.

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mjh2007 hit the nail on the head when he said that they're typically used with custom LCD glass.

You used the CC430 as an example; it's integrated into the TI Chronos watch, with a watch LCD on the face. See pages 75 (Schematic) and 83-84 (LCD information) of the watch manual for a description of this implementation. It uses its 24 segment pins and 4 'com' pins to drive those 24*4 = 96 LCD segments.

It's probably easier, though, to just get a dot-matrix display with an integrated controller. Do you have a source on a display without a controller?

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  • \$\begingroup\$ I don't think you can add more COM pins to the built in LCD module. \$\endgroup\$ – mjh2007 Oct 28 '10 at 19:57
  • \$\begingroup\$ So, does a 32x32 LCD glass actually have 1024 inputs, or are they wired in rows and columns and scanned? \$\endgroup\$ – Toby Jaffey Oct 28 '10 at 20:05
  • \$\begingroup\$ I don't have a specific display in mind, I'm just interested in low cost Tamagotchi type toys and the electronics in them. I assume they have a custom ASIC with built in LCD controller. But, I'm wondering how low cost a hobbyist can go? \$\endgroup\$ – Toby Jaffey Oct 28 '10 at 21:17
  • \$\begingroup\$ Microchip application note AN658 in the section titled "How are LCD Pannel's driven" may help you understand why you can't just add more COMs or Segments using regular digital I/O pins. \$\endgroup\$ – mjh2007 Oct 28 '10 at 21:47
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    \$\begingroup\$ Great link! You should put that in your answer. Was "The last time Microchip investigated high pin count packages, 30,000+ was not an option" a bit of HUMOR in an application note? Edited my answer, BTW. \$\endgroup\$ – Kevin Vermeer Oct 28 '10 at 21:53
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Non TFT LCDs consist of an array on pixels on the inside of usually the bottom glass of the glass sandwich.

The top glass can have 1, 2, 3 or 4 different backplanes, each backplane located directly across from a specific array of pixels. In the duplex mode (TWO BACKPLANES), 48 pins of the MCU drive both sets of 48 pixels each. The two backplanes are used to select which array of pixels is enabled. It's an optical multiplexing trick, that fools the human eye into seeing one large set of 96 pixels by multiplexing the two backplanes are 100 Hz or higher. Thus a 96 pixel display can be driven by 50 pins of the MCU (48 pixels plus two backplanes).

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