All 68HC05 "L" family members have liquid crystal display (LCD) interfaces of varying degrees of sophistication. A representative implementation is the LCD driver on the popular MC68HC705L16, shown in the block diagram above.
Supporting as many as 39 frontplanes and up to 4 backplanes, the MC68HC705L16 can drive up to 156 segments. Bias voltages for this LCD interface are input directly on the VDD, VLCD1, VLCD2, and VLCD3 pins, typically from taps off a resistive ladder network. Bias levels of 1/1, 1/2, 1/3, and 1/3 are used when driving one, two, three, and four backplanes, respectively. Uncommitted backplane pins may be used as discrete outputs. Similarly, separate enable and multiplexer control bits also allow independent configuration of frontplanes [38:27] as discrete outputs.
The MC68HC705L16 has two other notable features. Like other 68HC05 "L" family devices, it has an alternate low-power oscillator from which LCD waveform timing can be derived. Additionally, when the LCD interface is disabled, the register locations that comprise display RAM are still accessible and can be used to store variables or prepare new messages for display at a later time.
