Embedded systems frequently use HD44780-type LCD displays as it is considered the most popular alphanumeric display controller. The interface comprises at least 14 pins: eight for data, three for control (EN, WR, RS), two for power supply (Vdd, Vss), and one for contrast (Vre). Configured in 8-bit mode, it requires at least 10 I/O lines (D0..D7, EN, RS). Configured in 4-bit mode, it requires at least six I/O lines (D4..D7, EN, RS). This last case seems usable when using an 8-pin PICmicro. However, 8-pin PICmicros have one pin as an input-only pin.
Many solutions for expanding I/O pins have been described in EDN Design Ideas (references 1 to 3). In a pin-limited external embedded system, if an additionnal LCD display becomes necessary, instead of changing the microcontroller with more I/O lines, it is often better (in terms of cost, and to make development easier and faster) to use this LCD module with a dedicated 8-pin PICmicro and consider it as an intelligent display.
For more detail: One wire brings power & data to LCD module
