Source | Electronic Circuit Development Learning
Serial ports are familiar to friends in the electronics industry; they are a very common device communication protocol. Most desktop cases have RS232-DB9 interfaces, and they also have multiple USB ports. Laptops typically only have three USB ports and no DB9 ports. If you want to use serial port functions, you can only use a USB-TTL module.
If multiple serial ports are needed, it will occupy multiple USB ports. Coupled with the mouse, debugger, etc., the USB ports provided by the PC become insufficient.
This article shares several methods for single USB to multiple serial ports, where the serial ports are independent and do not interfere with each other.
1. CH9342 Single Chip for Dual Serial Ports
If you only need two serial ports at most, then CH9342 is a good choice. It is a single USB to dual serial port chip that provides two sets of full-duplex 9-wire asynchronous serial ports UART0/1, used to expand asynchronous serial ports for computers or upgrade ordinary serial devices to USB bus.
Evaluation board:
2. CH9344 Single Chip for 4 Serial Ports
If two serial ports are not enough, do not worry; we also have a 4 serial port chip. CH9344 is a single USB to 4 serial port control chip that provides 4 sets of full-duplex asynchronous serial ports UART0/1/2/3, used to expand asynchronous serial ports for computers or upgrade ordinary serial devices to USB bus.
Only a 30M crystal and a few capacitors are needed externally for use, supporting baud rates from 1200 to 7.8125Mbps, in LQFP-48 packaging.
Evaluation board:
3. CH934X + CH438 for Multiple Serial Ports
If more serial ports are needed, you can try using CH934X with CH438. CH943X is a USB to multiple serial port control chip that mainly handles all data transmission of the USB interface and operates CH438 through a parallel interface to achieve the reception and transmission of multiple serial port data.
After installing the driver, insert the USB to serial port module, and multiple serial ports will appear on the computer. These serial ports operate exactly like the computer’s built-in serial port, and each serial port is independent and does not interfere with each other. The application diagram for USB to multiple serial ports is as follows:
N can be 2, 4, 8, or 16, and the baud rate supports 1200-921600bps. Each serial port operates exactly like the computer’s built-in hardware serial port, independent and does not interfere with each other. There is no relevant application data found on the official website; it may be necessary to contact the manufacturer for information.
4. GL850G + Serial Chip for Multiple Serial Ports
With a 4 serial port chip, what if you want 6, 8, 12, or 16 serial port chips? It’s simple; you just need to add a USB Hub chip. GL850G is a USB 2.0 HUB chip, and many USB expanders on the market are based on this chip. It can expand 1 USB port into 4 USB ports at most.
To support serial port functions, we need to add a USB-TTL chip to each expanded USB port, which increases the selection of serial chips. Single serial ports include domestic CH340/CH341 series, and foreign ones like FT232, PL2303, CP2102, etc. The prices of these serial chips vary greatly, and the maximum supported baud rates also differ, so choose based on your needs. For multiple serial ports, there are CH9342 for 2 serial ports and CH9344 for 4 serial ports.
If you want to achieve multiple serial ports, you can refer to the following combination schemes:
6 serial ports: GL850G + 3 CH9342 chips
6 serial ports: GL850G + 1 CH9342 + 1 CH9344 chip
8 serial ports: GL850G + 2 CH9344 chips
Here is a shared application scheme based on GL850G for two serial port expansions + 1 USB. GL850G supports a maximum of 4 USB expansions, and I only used 3 of them, with 2 being serial ports and 1 being a USB female connector, which can be used for cascading two modules or connecting debuggers, mouse, keyboard, and other USB devices.
Finished product image:
Among them, CH340E is in MSOP-10 packaging, which is the smallest in the CH340 series. Additionally, Qin Heng has recently released the SOP-8 packaged CH340N, which only has 8 pins.
CH340 series:
References
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Stackable USB-UARTx2 Converter
http://st.avros.net/articles/usb_uartx2.html
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Qin Heng Microelectronics Official Website
http://www.wch.cn/products/category/1.html
Conclusion
The application method of GL850G Hub chip + serial chip is quite flexible, allowing for the expansion of serial ports while also expanding USB ports. The CH9344 application circuit is relatively simple, requiring only a single chip to achieve 4 serial ports.
When choosing among the above schemes, consider chip prices, the number of serial ports, baud rate ranges, etc. Of course, if it is for DIY use for debugging, it doesn’t matter much.
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