USB-to-UART vs USB-to-Serial? - Page 1
Forum section: electronics / beginners

author: casper.bang
author_rank: Frequent Contributor
timestamp: October 31, 2013, 11:12:42 am
content: I'm about to write some code for interfacing with an RFID/NFC/Mifare reader, which consists of aSilicon Labs CP2102USB-to-UART bridge IC, a Mifare RC522 RF chip and an ATMega8A sitting in between.I'm not fully well versed in chip interconnect technologies, so could a kind sound explain to me the difference between a USB-to-UART bridge like the mentioned CP2102 compared to a classic USB-to-serial bridge IC like i.e. a FTDI FT232? Can the USB-to-UART simply be seen as a subset of USB-to-serial, since serial usually also includes some RTS, DTS pins etc.?

author: Simon
author_rank: Unknown
timestamp: October 31, 2013, 11:15:03 am
content: I always thought usart and serial were the same thing but I'm no expert.

author: Bored@Work
author_rank: Super Contributor
timestamp: October 31, 2013, 11:23:41 am
content: Words are sometimes a bit muddy here.To UART(or if it is an Atmel device USART) means the conversion is to logic-level serial. The logic-level of the MCU.To serialcould mean it is to logic-level serial, or to real full RS232 voltages. The later ones being a bit impractical, because you can't directly connect RS232 to an MCU, you need an aditional level converter like a MAX232.

author: alxnik
author_rank: Regular Contributor
timestamp: October 31, 2013, 11:51:49 am
content: Indeed, words get muddy.UART and USART (also supports synchronous communication, haven't seen an application using it though) are lower level designs than what we actually know as serial or rs232 etc. In essence, they are shift registers. Over time more features were integrated in them such as hardware flow control or modem control signals (most popular device at the time). However UART/serial description may be interchangable. The most common chip in hardware serial devices in older PCs was a UART (16550) and the FTDI/prolific chips can be described as UARTs.Now about the CP2102, I use it to program arduinos and I know that it has modem control signals which for the arduino are used to auto-reset the atmega after programming. For all intended uses that I know of/have used in the past, CP2102 should be able to do the things that FTDI/prolific chips can do. The main difference is that CP2102 is cheeeep, (or probably cloned?) and usually used in lower end devices.

author: kayvee
author_rank: Regular Contributor
timestamp: October 31, 2013, 12:11:11 pm
content: The CP21xx and the FTDI devices are pretty much similar devices, but yes they do offer a price advantage over the FTDI for some reason. The CP2102 is pretty simple and straight forward to use.A number of years ago the CP2102 had the advantage over the FTDI as it had the internal oscillator whereas the FTDI required an external oscillator. However it was then only available in the QFN package which was less favoured for development/small scale/hobbyist uses.

author: casper.bang
author_rank: Frequent Contributor
timestamp: October 31, 2013, 12:20:37 pm
content: Quote from: alxnik on October 31, 2013, 11:51:49 amOk, so in my case then, the CP2102 is probably little more than a USB wrapper around the ATMega's own USART pins (I guess that would explain why I can identify port-speed commands to be used through the *existing* serial connection?!). Thanks guys for the quick feedback.