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I am going to use the HT16C21 LCD driver to drive my LCD.

Looking at the datasheet (in the "Pin Assignment" section), I noticed that the IC comes in 4 different packages, each with varying numbers of pins. The ones with fewer pins seem to exclude some LCD segment pins.

Despite the difference in pins, the datasheet does not mention anything about the difference, and it gives the impression that all the packages behave the same.

Am I missing something here? What is the functional difference between the different packages? Do all 4 behave identically?

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closed as unclear what you're asking by Chris Stratton, Elliot Alderson, Dmitry Grigoryev, Lior Bilia, Warren Hill Feb 7 at 10:12

Please clarify your specific problem or add additional details to highlight exactly what you need. As it's currently written, it’s hard to tell exactly what you're asking. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.

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    \$\begingroup\$ Pretty obviously, you can't use operations that rely on pins not present on a given package... \$\endgroup\$ – Chris Stratton Feb 3 at 20:48
  • \$\begingroup\$ @ChrisStratton but what is the functional difference? the datasheet does not mention any difference \$\endgroup\$ – eeze Feb 3 at 20:49
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    \$\begingroup\$ Again, you can not use functions which require pins that are not preset. It up to the system designer to determine what functions they require and select a package which provides the needed pins, just as it is up to that designer to make the connections which they have determined their application requires. Realistically you should probably not at present be trying to build a board with this chip, but for the moment instead stick to displays with integrated controllers, both as a matter of economics and until you are more familiar with these types of controllers. \$\endgroup\$ – Chris Stratton Feb 3 at 20:50
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This is an answer in general terms rather than specifically about this IC.

It's poor form for the manufacturer not to explicitly state the functional differences between the versions of the IC in different packages. But, as Rumsfeld would say, you design with the documentation you have, not the documentation you might wish to have. That is unless you are on good terms with a Field Application Engineer at the manufacturer, in which case you can ask her to clarify.

In the absence of other info, it's likely that all package variants use the same die, and those with "missing" pins simply leave some wire-bond pads on the die unconnected, so the IC will behave as though you had chosen one of the variants with all pins but had left some pins open-circuit. However, that isn't the only possibility. For instance, if there's some configuration input pin that the user is supposed to strap high or low and not leave floating, the IC manufacturer might use an internal bond wire to connect it to VCC or GND in a low-pin-count package variant and thereby not have to have a package pin for it, at the expense of configuration flexibility.

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"does not mention anything" except this:

Segment Driver Outputs

The LCD drive section includes 20 segment outputs SEG0 ~ SEG19 or 16 segment outputs SEG4 ~ SEG19 which should be connected directly to the LCD panel. The segment output signals are generated in accordance with the multiplexed column signals and with the data resident in the display latch. The unused segment outputs should be left open-circuit when less than 20 or 16 segment outputs are required.

Column Driver Outputs

The LCD drive section includes 4 column outputs COM0~COM3 or 8 column outputs COM0~COM7 which should be connected directly to the LCD panel. The column output signals are generated in accordance with the selected LCD drive mode. The unused column outputs should be left open-circuit if less than 4 or 8 column outputs are required.

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