Tech Blog

金鹏 Analysis: What Are the Differences in Connection Methods Between Serial Screens and Traditional Parallel LCD Screens?

金鹏 Analysis: What Are the Differences in Connection Methods Between Serial Screens and Traditional Parallel LCD Screens?

The core difference between serial screens and traditional parallel LCD screens lies in their different data transmission paths and control methods: serial screens usually send commands and data through UART, RS-232, RS-485, or other serial interfaces using fewer signal lines; traditional parallel LCD screens rely on parallel buses such as 8080, 6800, and RGB, while using multiple data lines and timing control lines to transmit images. Simply put, serial screens have simpler connections, while parallel LCD screens rely more on the timing design and interface resources of the host controller.

  • Serial screen: Transmits data bit by bit through a serial interface; common interfaces include UART, RS-232, and RS-485.
  • Parallel LCD screen: Transmits multiple data bits simultaneously through multiple data lines; common interfaces include 8080, 6800, and RGB.
  • Core difference: Serial screens save more host controller interface and wiring resources; parallel LCD screens are better suited for direct pixel control and high-speed refresh by the host controller.

1. Different Numbers of Connection Lines and Interface Definitions

The “serial port” of a serial screen refers to a communication interface that transmits data sequentially, bit by bit. Simply put, a serial port is like a single-lane data channel, through which data passes in order. Taking common UART as an example, the system usually needs to connect TX, RX, and GND; if RS-485 is used, two differential signal lines, A and B, may also be used. UART is short for “Universal Asynchronous Receiver/Transmitter” and is responsible for transmitting and receiving data according to an agreed baud rate and data format; differential signals transmit information through the voltage difference between two lines, and their anti-interference capability is usually better than that of single-ended signals.

According to the TIA-232-F “Interface Between Data Terminal Equipment and Data Circuit-Terminating Equipment” standard, the RS-232 interface includes clear electrical level and signal definitions; in actual connections, level matching, grounding, and communication direction still need to be considered. RS-232 is a single-ended serial communication standard, usually suitable for point-to-point connections; RS-485 is a serial communication standard using differential transmission, more suitable for industrial sites and longer-distance communication.

Parallel LCD screens, by contrast, use multiple signal lines for parallel transmission. For example:

  • RGB565 interface usually requires 16 data lines, plus control signals such as pixel clock, HSYNC, VSYNC, and data enable.
  • RGB888 interface may require 24 data lines and can transmit richer color information.
  • 8080 and 6800 interfaces usually also require control signals such as chip select, read/write, and data/command selection.

The exact number of pins varies depending on screen resolution, color depth, and controller solution; when selecting, refer to the screen datasheet.

From a wiring perspective:

  • Serial screens reduce the number of cables and are suitable for scenarios with fewer controller interfaces, limited device space, or long-distance wiring.
  • Parallel LCD screens have more lines, so PCB layout needs attention to length matching, impedance, crosstalk, and timing relationships.
  • For related design, refer to the display controller manufacturer’s hardware design guide and the screen manufacturer’s original specifications.

2. Different Data Transmission Methods and Host Controller Loads

For serial screens, the screen’s internal controller usually handles font libraries, widgets, page switching, and some graphics processing. The host controller device only needs to send commands such as “switch page” and “update value”; it does not need to continuously refresh the entire screen. Here, “widgets” refers to directly callable UI elements such as buttons, text boxes, and progress bars; “font library” refers to the font data set inside the screen used for displaying text.

Taking 115200 bit/s, 8N1 format as an example, each byte usually occupies 10 bits, and the theoretical effective transmission capacity is approximately:

  • 115200 ÷ 10 = 11520 Byte/s;
  • that is, approximately 11.52 KB/s;
  • of which 8 bits are effective data, while 1 start bit and 1 stop bit are transmission overhead.

This calculation is based on the common UART 8N1 data format; actual speed is also affected by protocol frames, checksums, and response mechanisms.
Source: The bit structure of 8N1 is based on the general data frame definition of UART communication; the specific baud rate and frame format should be subject to the serial screen product communication protocol or datasheet.

Traditional parallel LCD screens often require the host controller to continuously provide pixel data and synchronization timing. Here, “pixel timing” refers to the time coordination among signals such as pixel clock, HSYNC, VSYNC, and blanking intervals; if the host controller is configured incorrectly, problems such as garbled display, offset, or failure to light up may occur.

Taking 800×480, 60 Hz, RGB888 as an example, calculated only by the effective display area:

  • 800 × 480 × 60 × 24 = 552.96 Mbit/s;
  • converted, this is approximately 69.12 MB/s;
  • after adding blanking intervals, the actual interface bandwidth will be even higher.

This value is an engineering calculation result and is for interface evaluation reference only; actual bandwidth should be confirmed according to screen timing parameters.
Source: The above data is calculated based on an 800×480 resolution, 60 Hz refresh rate, and 24-bit color depth; actual timing parameters should be subject to the LCD screen manufacturer’s original specifications.

According to the design philosophy embodied in the “Display Serial Interface Specification” published by MIPI Alliance, display interfaces need to balance bandwidth, pin count, and power consumption. MIPI DSI is a high-speed serial interface for display devices, usually transmitting large-scale image data through fewer differential lanes.

For different application scenarios, key considerations include:

  • Devices requiring fast full-screen animation, video playback, or high-refresh-rate display should focus on evaluating parallel interfaces or high-speed dedicated display interfaces.
  • For instrumentation, industrial control, and human-machine interfaces, serial screens can often reduce the difficulty of host controller software development.
  • If the interface mainly displays parameters, status, and buttons and does not need continuous refresh of the entire screen, serial screens are usually easier to implement.

3. Different Development Processes, Anti-Interference, and Application Choices

The development focus of serial screens is the communication protocol, including:

  • Baud rate: indicates the symbol rate transmitted per unit time, commonly expressed in bit/s.
  • Data format: includes data bits, parity bit, and stop bit, etc.
  • Frame header and length: used to identify the start position and data length of a complete command.
  • Checksum: used to check whether an error has occurred in transmitted data.
  • Timeout handling: when no response is received within a specified time, the program takes measures such as retransmission or error reporting.

When using RS-485, it is also necessary to follow the TIA-485-A standard and pay attention to differential transmission, termination resistors, and bus topology. A termination resistor is a matching resistor connected at the end of the communication bus to reduce signal reflection; bus topology is the way devices are connected on the line. In industrial sites, it is recommended to avoid long-distance star wiring and to adjust the communication rate according to cable length and environmental interference.

The development focus of parallel LCD screens is controller initialization, display memory management, and display timing. Display memory is the storage area used to temporarily hold image pixel data; the host controller needs to correctly configure:

  • Pixel clock;
  • HSYNC and VSYNC;
  • Blanking parameters such as front porch and back porch;
  • Data bit width and color format.

Otherwise, problems such as garbled display, offset, or failure to light up may occur. VESA-related display timing materials and the screen manufacturer’s original specifications are usually important sources for confirming these parameters.
Source: VESA display timing materials, display controller manufacturer hardware design guides, and LCD screen manufacturer original specifications.

According to the IEC 61131-3 programming standard in the industrial automation field, control systems emphasize program structure, maintainability, and device collaboration. In display projects, this corresponds to:

  • Serial screens can moderately separate interface logic from low-level control logic, making it easier to modify pages later.
  • Parallel solutions are better suited to products that require the host controller to directly control each pixel and pursue real-time rendering.
  • For industrial site applications, electromagnetic interference, communication distance, maintenance difficulty, and device upgrade methods should also be comprehensively considered.

4. Selection Recommendations for 金鹏 Serial Screens

金鹏 serial screens are suitable for devices that need fewer connection lines and shorter interface development cycles, such as industrial instruments, control cabinets, testing equipment, and small human-machine interfaces. During selection, key items to verify include:

  • Communication interface type, such as UART, RS-232, or RS-485;
  • Operating voltage and power supply method;
  • Baud rate range and communication protocol;
  • Screen resolution, size, and visible area;
  • Whether custom pages, font libraries, and widgets are supported;
  • Installation dimensions, cable definitions, and environmental adaptability.

Specifically:

  • If the device only needs to display parameters, alarm status, and operation buttons, serial screens should be given priority.
  • If the application requires high-frame-rate images, continuous video, or large-capacity full-screen refresh, focus on evaluating parallel interface bandwidth, host controller performance, and PCB wiring capability.
  • If the device is in an industrial site, also focus on verifying the RS-485 wiring method, termination matching, and anti-interference performance.
  • If the interface needs to be modified frequently later, serial screens are usually more conducive to separating interface design from the host controller program.

The final solution should be based on 金鹏 product specifications, interface definitions, and actual communication test results; the above rate and bandwidth data are for engineering design reference only.