PORTS Forum

Ports and Interfaces => Serial Ports => Topic started by: lrinetti on October 06, 2013, 12:03:12 pm

Title: RS232 t USB
Post by: lrinetti on October 06, 2013, 12:03:12 pm

What is the difference between an USB to RS232 adapter (the most common kind of adapter) and an RS232 to USB adapter ?
My understanding is that the RS232 to USB adapter should have a behaviour like a host but i'm not sure.

Regards
luciano

Title: Re: RS232 t USB
Post by: Jan Axelson on October 06, 2013, 01:08:12 pm

Every commercial USB/RS-232 adapter I've seen attaches to the host computer via USB and attaches to a device or other computer via RS-232.

If you wanted to do it the other way around, you would need an embedded system with USB host capabilities, an RS-232 port, and firmware to manage the data.

Title: Re: RS232 t USB
Post by: lrinetti on October 06, 2013, 01:39:14 pm

Thank You for the answer.
I am in the second case: i need all the items: embedded system, firmware, etc.
Given my little experience, i only ask you to address me to a simple embedded system that let me build a basic working sistem with RS232.

Title: Re: RS232 t USB
Post by: Jan Axelson on October 06, 2013, 02:47:15 pm

The BeagleBoard has USB host support and async serial that can convert to RS-232:

http://elinux.org/BeagleBoard
http://www.janaxelson.com/beagleboard.htm

Also see:

http://www.janaxelson.com/embedded_host.htm#chips

Title: Re: RS232 t USB
Post by: EagleWolf on October 07, 2013, 08:59:13 am

In my experience in adapter terms everything is termed as
"From ---> To" sort of formatting.
USBtoRS232 would be From USB at the computer to Serial Port (RS232) at the device attached.
RS232toUSB (never seen one of these) would be the other way around.

Title: Re: RS232 t USB
Post by: ruutboy on November 24, 2013, 10:37:38 am

If you want it to be the host, then if I'm not mistaken, that would be USB OTG (On The Go). Otherwise, aren't we just talking about a USB to TTL converter?

Title: Re: RS232 t USB
Post by: Jan Axelson on November 24, 2013, 01:18:48 pm

OTG is one option, but USB embedded hosts don't have to support OTG.

Title: Re: RS232 t USB
Post by: ruutboy on November 24, 2013, 05:01:49 pm

Okay, so aren't we just talking about a USB to TTL converter then? It's bi-directional after all. What would be the distinction of the driving vs. driven end of it?

Title: Re: RS232 t USB
Post by: Jan Axelson on November 24, 2013, 05:39:55 pm

A USB host has to manage the bus and provide power. According to the USB Embedded Host and OTG spec, an embedded host doesn't have to do everything that a full USB host is required to do but still must perform the functions of a USB host. Mainly an embedded host can support a smaller subset of devices.

Title: Re: RS232 t USB
Post by: ruutboy on November 24, 2013, 08:11:18 pm

Ahh, ok. It's something that I will have to play around with.