Re: Communication over usb serial cable
Re: Communication over usb serial cable
- Subject: Re: Communication over usb serial cable
- From: "Rakesh Singhal" <email@hidden>
- Date: Fri, 5 Dec 2008 17:24:14 +0530
Hi Terry,
Thanks a lot. I configured everything properly except handshaking and
by mistake I modified c_cflag instead of c_iflag. now it is working.
Sorry to trouble you. Now it is working fine.
Regards
rksinghal
On Fri, Dec 5, 2008 at 5:07 PM, Terry Lambert <email@hidden> wrote:
> On Dec 5, 2008, at 12:01 AM, Rakesh Singhal wrote:
>>
>> I am not sure that this is the proper list to put my query. I have
>> connected my windows system to Mac using usb serial cable.
>>
>> mac ----- usb port <-----> usb serial cable <-----> serial port ----
>> windows
>>
>> First case where I am using ZTerm utility on Mac to communicate with
>> Hyper terminal on windows. I configured and it is working properly.
>>
>> Second case, I have my application instead of ZTerm utility and I
>> configured. Now when I send any data from hyper terminal, I get it in
>> my application on Mac but not in proper format. Like if I press C in
>> Hyper terminal, it shows #? (2 bytes) in Mac.
>>
>> Please suggest what I am missing here so that at least I am able to
>> get proper data like ZTerm.
>>
>> Configuration details:
>>
>> baud - 115200
>> stop bit - 1
>> parity - NO
>> data bits - 8
>> enable CLOCAL and CREAD.
>>
>>
>> One more thing if I check my application with any modem attached on
>> Mac only then I get the proper response of command like ATI etc.
>
>
> CLOCAL and CREAD are irrelevant; CLOCAL simply means you do ignore modem
> status lines, and CREAD simply means you will allow receives.
>
> Different or multiple characters received with a single character
> transmitted is typically an indication that the receive baud rate is higher
> than the transmit baud rate, and therefore there is sampling occurring.
> Very old systems with tightly controlled UART parts used for their
> implementation used to used this technique to recognize the baud rate of
> inbound modem connections by comparing the sample bit pattern vs. the known
> sample patterns for the CR character at various known baud rates well below
> the sample baud rate; hit return a couple of times, and "presto! login: " at
> the right baud rate.
>
> It can also typically happen if the bit framing is off - e.g. when you tell
> it to use other than 8 bits of data, either by mistakenly specifying
> something other than 7 bits with some type of parity, or specifying
> something other than 8 bits with no parity, or you've set the wrong number
> of stop bits, etc..
>
> With a little hand-waving, if your example of 'C' is an actual example, and
> we assume that the '?' was representing an unprintable character from line
> garbage or you hiting areturn character after the 'C', and the '#' was
> representing a printable '#' then:
>
> C 0x43 01000011
> # 0x23 00100011
>
> strongly implies that the bits are being time-compressed, implicating that
> the transmit baud rate is higher than the receive baud rate.
>
> I'd suggest either looking at the source code for known working programs
> (Apple supplies 'cu', 'uucp', and similar programs in source form), or
> finding a book or guide online, such as:
>
> <http://www.easysw.com/~mike/serial/
> or
> <http://digilander.libero.it/robang/rubrica/serial.htm>
>
> to use as a starting point on UNIX serial programming, since you probably at
> least have your baud rate set wrong.
>
> Note that the above referenced material plays things a little loose with
> standards-controlled definitions, but has good UNIX programming information.
>
> -- Terry
>
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