I want to know the "internal parts of an LCD"... but I can't find any from the results.
"....according to the ASCII"
does that mean ASCII is stored somewhere in the LCD (e.g. ASCII stored in EEPROM) ?
Most displays of this type use the Hitachi HD44780 LCD controller, or something compatible. The HD44780 stores characters graphics in a 9920-bit mask ROM. (This appears near the bottom of the block diagram on page 3 of the datasheet.)
Some HD44780-compatible graphical LCDs (often sold as the "12864") will read a character table from an EEPROM attached to the back of the LCD. This is necessary because these LCDs support a Chinese font which is too large to store in mask ROM. I've been unable to find an English datasheet for the controller(s?) used on these displays, though.