USB to Serial Port Adapters, chips and adapters

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USB to Serial Port Adapters

There are several devices on the market to bridge the gap from a serial port (UART, SCI...) on your MCU to the USB bus. This page isn’t intended to discuss the end user USB products for adding a RS-232 port to your Macintosh, but much of the information below applies to them. Below is some information on some of the USB to RS-232 adapters I am aware of.

FTDI (Future Technology Devices International) produces several chips:

FT232H - Single Channel High Speed USB to Multipurpose UART/FIFO IC

FT2232H - Hi-Speed USB 2.0 - Dual UART/FIFO /I2C/SPI/JTAG IC up to 12 megabaud

FT4232H - Hi-Speed USB 2.0 - Quad UART Converter

FT230 - Full speed low cost

FT232R – Single USB 2.0 to Serial UART Converter IC.

FT2232D/C/L - Dual High Speed USB to UART/FIFO

FT232B – Single USB to UART Converter ICs

Most support arbitrary baud rates, so non-standard baud rates, like 3030 baud (used by Lionel) or 10417 baud (for the automotive LIN bus, see SAE specification J2602) are obtainable. FTDI has two different drivers available for their chips which can cause a problem on OS X systems. According to a FTDI FAE:

“With Mac OS X, our VCP and D2XX drivers are mutually exclusive.  You can only have one driver installed at a time.

With Linux and Windows, you can have both drivers installed with no problems”.

So this is a major pain in the neck if you don’t understand what is going on.

Prolific produces two devices:

PL-2303HX-Edition(Rev D)


Their drivers do not support arbitrary baud rates. They seem to be limited to this list found in this code found on Prolific’s web site.

75, 150, 300, 600, 1200, 1800, 2400, 3600, 4800, 7200, 9600, 14400, 19200, 28800, 38400, 57600, 115200, 230400, 460800, 614400, 921600, 1228800, 2457600, 3000000, 6000000

The newer Rev D device also supports 12,000,000 baud.

I have found the driver download doesn’t do 9600 & 19200 baud correctly on OS X 10.9 or 10.10.

Texas Instruments offers this one with OS X drivers:


This device has been around for a long time. The SLLA170F document describes the drivers and TI’s support. The drivers can be downloaded from:




CYUSBS232, CYUSBS234, and CYUSBS236 with asynchronous serial, I2C, and SPI support.

OS X compatibility note:

For FX2 on OS X:

Silicon Labs

The CP2110 data sheet is here:

Support is described here:

Driver download:

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USB to Serial Port Adapters

Lemos International

RS-422 with jumpers for echo, termination, and slew rate options. Based on the FTDI chip.

Other Hardware


USB to IrDA 1.4 adapter. One meter range. Up to 9600 Baud.

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