USB UART

Introduction

USB

USB

RS (Regular Standard) communications was the mainstay for system to machine communication for a long time. In many industry applications it still holds ground. At some point the rivalry was between parallel port communication and RS232. Parallel ports were hooked up to dot matrix printers and then data collection printed directly to hard copy.

USB came on the scene and this presented a problem for the embedded application since so much code out there worked so well with a serial port; would we now have to rewrite code to accommodate the USB interface.

The need to do so immediately was and has been negated by the release if what is known as a USB to UART bridge. This is a very clever little device that lets your PC believe that it’s talking o a USB device and the embedded device thinks it’s talking to a RS232 enabled port.

The two types that we haveĀ  used in designs is the FTR232 from FTDI and more recently the MCP2200 from Microchip. The FTR232 was easier to integrate with a windows PC, as the MCP2200 required a bit more coaxing with the need to perform a driver update.

Recently, FTDI released a new range of USB UARTS, the FT230x and the FT231X. The FT230X has a smaller profile and fewer of the traditional RS232 control lines. They are also allot cheaper than the previous FTR232 devices

Performance wise and useability there has not been much noticeable difference between the two except that the Microchip MCP2200 was much cheaper to obtain and does offer the advantage of GP based I/O.

8 Bits of data is still transferred between the embedded device and the PC host. If therefore you have a PC based application which captures the data sent from the PCB or received by the PCB these will function as per normal

From a PC usability perspective both emulators surface as normal comports or CDC devices and the system carries on unabated. There is no noticeable difference between a normal hardware based COM port and the emulated one.

The ZarDynamix Development PCBs are all communications enabled using either the FTR232 or the MCP 2200. When the new Munio PCB is release they will use the FT230X.

Usage

Trying to use these devices can be logistically intimidating as they are all supplied in SMD packages. If you are a genius with a soldering iron then it’s no problem. If you are not, many vendors have produced ‘break out board’ which is simply a small PCB which contains the USB Device and only the circuitry it needs. Usually there is a small header and this allows it to be connected to a bread board. These can be obtained for a few dollars.

[E]