Electronic – How to test if it is a non-multiplexed (static) LCD

You identified the LCD as being multiplexed—which it very likely is—so the AC you're seeing is probably just some segment being sequenced.

A microcontroller toggling pins in succession will indeed produce AC, however calling "x V AC" that is an extreme red herring. It is better described as a multiplexed signal with such a frequency and some voltage (amplitude, not AC voltage as measured by a meter).

Atmel's app note AVR340: Direct Driving of LCD Using General Purpose IO may be of use to you. This portion describes the "AC" that you're seeing and shows why.

To energize a segment, the waveform to that segment must be 180 degrees out of phase with its COM waveform. The voltage difference between the segment and COM signals will therefore be typically 5 Volts AC, which causes the segment to become visible after 300-400 msec of refresh cycles.

To de-energize (turn off) a segment, the COM and segment waveforms should be in phase with each other while that segment’s COM is active, that is, not at 2.5 volts. So, a LCD with all segments OFF will have the segment inputs IN PHASE with each COM input. (COM3 was omitted from Figure 2-2, since only 4 channels were available.)

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)