I have used graphic and alphanumeric LCDs. I have come across LCD Display Drivers & LCD Display Controllers ICs. When are they needed and what do they do?
Electronic – What are LCD Display Drivers & LCD Display Controllers? What are their applications
embeddedlcd
Related Solutions
The problem with using a microcontroller to drive an LCD is that an LCD requires constant attention. This can be mitigated with a CPLD driven over SPI (using DMA, of course), but then you run into the other problem: Color LCDs require a lot of data. 320x240 in black and white is marginal at 9.6KB, but make it 24 bit color and suddenly you need to deliver 230KB of data in 1/60th of a second. (Don't forget, though, that you can get 4-bit, 16-color control just by tieing the low 20 bits to one setting). A 24-bit frame buffer no longer fits in onboard RAM on most microcontrollers, and you probably don't have time to read from an external RAM chip, clock the data out, and still do other processing. Trying to do this with a CPLD (or an FPGA) and a RAM chip gets you well over the $2 price that caused you to balk in your question.
The traditional solution to interfacing a microcontroller with a color LCD is a display controller like an SSD1963. Here's a very simple block diagram:
Parallel input to a big RAM frame buffer (Translation: More than $2) interfaced with a register-configurable parallel LCD interface. The parallel input is usually compatible with a memory bus interface.
The color LCD market is not always easy to find on the web, usually being the domain of OEMs only, with the rest buying displays from companies who integrate the controller with the display. The best resource I've found has been Crystal Fontz, specifically this page on choosing graphic LCDs. Scroll to the bottom for the controllers, which include the following options (note: Not all are color controllers):
- Epson S1D13521B01 E Ink Broadsheet (1 module)
- Epson S1D13700 (11 modules)
- Epson SED1520 Compatible (8 modules)
- Himax HX8345 Compatible (1 module)
- ILITek ILI9325 Compatible (3 modules)
- KS0107/KS0108 Compatible (26 modules)
- Novatek NT7534 (14 modules)
- Orise Technology OTM2201A (1 module)
- Orise Technology SPFD5420A (1 module)
- RAiO RA8835 (1 module)
- Sanyo LC7981 (13 modules)
- Sino Wealth SH1101A (2 modules)
- Sitronix ST7920 (29 modules)
- Solomon SSD1303 (1 module)
- Solomon SSD1305 (9 modules)
- Solomon SSD1325 (2 modules)
- Solomon SSD1332 (1 module)
- Solomon SSD2119 (2 modules)
- ST STV8105 (1 module)
- Toshiba T6963 (23 modules)
Since you're looking for something with only a few digits, you don't need it to have its own controller. Try looking for LCDs called "bare glass". Those are just the LCD with the segments brought out to pins or contacts intended for zebra strip connectors.
If you use one of these, you will have to drive it yourself. It's not like a LED display where each segment is turned on to display it and off to not. LCD segments are driven with AC, and must not experience any net DC. Fortunately there are various microcontrollers that have such LCD drivers built in. For example, Microchip usually puts a "9" near the end of the PIC model number to indicate the LCD driver. Once you set up the LCD driver peripheral, you get a bunch of bits in memory that you can set or clear that directly map to LCD segments being displayed or not. The 7-segment generation if you want to display numeric digits is up to you.
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Best Answer
Display controllers receive high-level instructions from upstream ("draw the text 'ABC123' at the current position"), process/store them, and generates low-level instructions ("turn on pixels/segments X, Y, and Z").
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Display drivers receive low-level instructions and turn them into waveforms for controlling commons and segments ("enable common 3, disable others, and turn on pixels 3, 7, and 12").