Discussion:
USB - RS232
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Ting Xing
2010-04-07 00:10:17 UTC
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Hello,

I dont know if its appropriate to post such a topic here.
But any kind of advice will be appreciated.

My question is whether parallel access to multiple RS232 ports
expanded by using USB-RS232 converters is possible.

This is the details:
My computer communicates to several instruments through RS232. Because
there is only 1 RS232C port in a modern computer, I have to add extra
ports. I am now considering using USB to RS232 converts to realize it.
But due to the serial inherence of USB, I doubt I can not access two
different USB-expanded ports simultaneously.

Is my guess true?

Thanks in advance.

Ting
r norman
2010-04-07 01:48:22 UTC
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On Tue, 6 Apr 2010 17:10:17 -0700 (PDT), Ting Xing
Post by Ting Xing
Hello,
I dont know if its appropriate to post such a topic here.
But any kind of advice will be appreciated.
My question is whether parallel access to multiple RS232 ports
expanded by using USB-RS232 converters is possible.
My computer communicates to several instruments through RS232. Because
there is only 1 RS232C port in a modern computer, I have to add extra
ports. I am now considering using USB to RS232 converts to realize it.
But due to the serial inherence of USB, I doubt I can not access two
different USB-expanded ports simultaneously.
Is my guess true?
Thanks in advance.
Ting
My experience is that USB-serial devices when installed have drivers
that emulate ordinary COM ports. You can put as many as you want as
long as you configure them to occupy different COM port numbers. How
to do that is up to the USB device manufacturer.

My applications that were built to run on standard COM ports in old
fashioned system expansion cards and then the PCMCIA cards run with no
change on systems that use USB-serial ports set to use multiple COM
port numbers.
Ting Xing
2010-04-07 04:46:11 UTC
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Yes, USB-RS232 converts make port expansion easy and agile.

But I wonder, if two "session" of communications can work
simultaneously.

For example, COM2 and COM3 are ports expanded using USB converters.
And I want to transmit 9600bits to COM2 and COM3 respectively.
Assuming both ports work under 9600bps, can transmittance on both
ports
finish in about 1 second?

Ting
r norman
2010-04-07 05:05:29 UTC
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On Tue, 6 Apr 2010 21:46:11 -0700 (PDT), Ting Xing
Post by Ting Xing
Yes, USB-RS232 converts make port expansion easy and agile.
But I wonder, if two "session" of communications can work
simultaneously.
For example, COM2 and COM3 are ports expanded using USB converters.
And I want to transmit 9600bits to COM2 and COM3 respectively.
Assuming both ports work under 9600bps, can transmittance on both
ports
finish in about 1 second?
There is no problem using the COM ports simultaneously. It is no
different than using two COM ports in the old-fashioned plug-in board
system.
Ting Xing
2010-04-08 04:08:42 UTC
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Thank you very much for the replay.

Maybe USB cable works in some way similar to an ether net?

Ting
Pavel A.
2010-04-12 20:06:43 UTC
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Post by Ting Xing
Thank you very much for the replay.
Maybe USB cable works in some way similar to an ether net?
No, USB cable is not similar to ethernet, and not similar to RS232 cable.
The timing of transferring your data will be different (USB can add
latency),
so if your application is sensitive to exact timing, it may stop working.
Test it.

-- pa
Ting Xing
2010-04-13 06:46:33 UTC
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Thank you very much for the information.

But except for latency, I guess multiple "sessions" of RS232
transferring can work simultaneously.

For example, sending 9600 bits to both COM2 and COM3 might finish
within about 1 second at 9600 bps.
Because USB's transferring speed is much greater than 9600bps.
The premise is bit transferring of COM2 and COM3 can be interleaved: 1
bit to USB COM2, then 1 bit to USB COM3,
1 bit to COM2, ......

Is there any USB group to find more information?

Ting
Anthony Wieser
2010-04-13 07:40:12 UTC
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Post by Ting Xing
Thank you very much for the information.
But except for latency, I guess multiple "sessions" of RS232
transferring can work simultaneously.
For example, sending 9600 bits to both COM2 and COM3 might finish
within about 1 second at 9600 bps.
Because USB's transferring speed is much greater than 9600bps.
The premise is bit transferring of COM2 and COM3 can be interleaved: 1
bit to USB COM2, then 1 bit to USB COM3,
1 bit to COM2, ......
Is there any USB group to find more information?
Ting
You might try one of the big manufacturers' websites, like for example
www.ftdichip.com

We've used these in some of our products.

--
Anthony Wieser
Wieser Software Ltd
m
2010-04-13 23:06:48 UTC
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yes - multiple IOPs can be in progress simultaneously. A better analog for
the Universal Serial Bus (USB) then Ethernet is the PCI bus. Physically
they are quite different, but logically they are both busses connecting
multiple peripheral devices. In your case, the devices are serial
controllers, and the fact that data is sent and received via a USB cable
rather than solder on the motherboard is mostly irrelevant (only important
if there are strict latency / jitter requirements, but this is true of any
physical topology)
Post by Ting Xing
Thank you very much for the information.
But except for latency, I guess multiple "sessions" of RS232
transferring can work simultaneously.
For example, sending 9600 bits to both COM2 and COM3 might finish
within about 1 second at 9600 bps.
Because USB's transferring speed is much greater than 9600bps.
The premise is bit transferring of COM2 and COM3 can be interleaved: 1
bit to USB COM2, then 1 bit to USB COM3,
1 bit to COM2, ......
Is there any USB group to find more information?
Ting
Ting Xing
2010-04-08 04:08:51 UTC
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Thank you very much for the replay.

Maybe USB cable works in some way similar to an ether net?

Ting
Ting Xing
2010-04-08 04:10:35 UTC
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Thank you very much for the reply.

Maybe USB cable works in some way similar to an ether net?

Ting
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