Serial vs. Parallel

Serial vs. Parallel

Understanding Parallel and Serial Interfaces

There are two types of interface modes for LCD’s, serial and parallel. Some LCD’s offer both interface modes while some are exclusively one type. Each interface type has their own advantages and disadvantages. You may be wondering which is the best interface for your project or what each of them consist of before deciding on your next LCD. This is a brief guide summarizing the main points of each interface mode.

The main difference between the serial and parallel interfaces is how they transmit data. In serial interface the data is sent or received one bit at a time over a series of clock pulses. In parallel mode the interface sends and receives 4 bits, 8 bits, or 16 bits of data at a time over multiple transmission lines. These two interface modes will be explained in further detail below.

Serial Interface

The serial interface is a bi-directional data bus that transmits a series of 8-bits in parity, each with a set clock pulse width, and one at a time. For this reason, serial interface transmission can often be slower (but cheaper) than parallel transmission. Serial interface LCD’s controllers require fewer connection pins than the parallel interface. This makes connecting to an external processor (such as a microcontroller) easier.

Serial interfaces consist of 3 types each with their own pins:

  1. I2C (Inter-Integrated Circuit): Serial Data In and Serial Clock
  2. 3/4-wire SPI (Serial Peripheral Interface): Consists of Serial Data Out, Serial Data In, Serial Clock and an additional Chip Select pin for the 4-wire SPI
  3. Serial synchronous control and data lines: Serial Data In, Register Select, Reset, and Serial Clock

Below is a Serial Interface connection example:

Serial Interface Pros:

  • Less data pins
  • Cheaper
  • Easy setup

Parallel Interface

The parallel interface transmits 8-bits, or one byte, of data over multiple data bus lines over one clock pulse. This makes parallel transmission faster than serial but is typically more expensive and requires more data pins to be connected. The parallel interface consists of 8 data pins and 3 control pins. The control pins are typically labeled: Register Select (RS), Enable (E), and Read/Write (R/W). Additional common parallel interface pins may include: Contrast adjust (V0), Chip Select (CS) and

Parallel interface consists of 2 standard types:

  1. 8080 type: parallel 4-bit/8-bit data input with a write and a read line
  2. 6800 type: parallel 4/8-bit data input with write, read and enable lines

Below is a parallel interface connection example:

Parallel Interface Pros

  • Faster data transmission
  • High performance


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