On 9/2/2010 11:27 PM, Anti-Spam wrote:
On Thu, 02 Sep 2010 16:26:50 -0600, hamilton<hamilton_at_nothere.com
wrote:
On 9/2/2010 2:51 PM, Anti-Spam wrote:
On Thu, 02 Sep 2010 16:25:16 -0400, Rich Webb
bbew.ar_at_mapson.nozirev.ten> wrote:
On Thu, 02 Sep 2010 21:30:57 +0200, Anti-Spam<Anti_at_Spam.com> wrote:
Probably been covered a thousand times in this forum, but have been
doing other things for quite a few years now. I designed many years
ago some Serial interface boards using the MAX232CPE RS232 chip. I
have been asked by the owners of the product to change these to USB
connectivety. The FTD chips obviousley come to mind for such a task,
but need some help please. We would like to replace the RS232 port
with a USB port. What I would ideally like to do, is remove the MAX
chip altogether and replace it with a FTD chip. The problem for me is
that I did not write the Firmware for this project, so I am not in a
position to change anything as far as the Microcontroller Programming
is concerned (we do not have the source code). We use on the MAX chip
Tx, Rx and the CTS, RTS lines.
What we would like to achieve is for the end customer for the
interface board, to be able to load the FTD drivers, connect using the
USB port, and use the board like nothing had changed. Is this
possible?
Yes, it is. It's also possible that it won't work at all.
If the RTS/CTS lines are used "as intended," that is, for serial flow
control, then the probability that it will work correctly and
transparently is very high, approaching 1.
If, however, the RTS/CTS pair are used as a "side channel" for signaling
and if the signals are required to be synchronized with the serial data
stream or with each other, then you may have a problem.
One other possible problem is that some applications limit the number of
COM ports that they can "see." For example, the FlukeView software for
their ScopeMeters will only connect up through COM8. USB serial ports,
on the other hand, can be up in much higher-numbered ports depending on
how many different USB-serial gadgets a given machine has used in the
past.
It is possible to work around this, if necessary, by going into the
Windows Device Manager and manually assigning a "visible" COM port
number to a particular USB-serial instance. In this case, the change
from a hardware RS-232 port to a virtual USB-serial port would work
(subject to the RTS/CTS caveats above) but could require the end user to
take an extra step or two to set it up.
The guy who wrote the Firmware for this project was an older, very
serious Polish guy, so the CTS and RTS implimentation was more than
probably, text book RS232 implimentation.
The embedded side won't be a problem.
Does this board connect to a PC ??
If so, does the PC software toggle the CTS/RTS lines by writing the I/O
ports on the PC buss ??
If this is true, you will not be able to use a USB serial port.
You will need to re-write the PC software.
h
Thanks, do you have any example circuits?
I do not think you understand my statement.
You will need to re-write your PC software.
There is no schematic for PC software.
In another post you said:
"What we would like to achieve if possible, is for existing customers
to carry on using the product without change to the software they have
had written for their host PC."
The "if possible" is what I am telling you.
Its not.
Unless you know if the person who wrote the PC software did not use
direct PC I/O port calls in his code.
By the sounds of it, you do not know.
With the information given, you can not just replace a hardware serial
port on a PC with a USB serial port and expect it to work without problems.
controls the COM port through the Windows API. GetCommState() and
