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rs232 problem

 
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UU
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rs232 problem
PostPosted: Sat Apr 15, 2006 11:27 am     Reply with quote
do i need a rs232 level shifter for connecting a the pic from the millenium board to a GSM modem
jecottrell



Joined: 16 Jan 2005
Posts: 559
Location: Tucson, AZ

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PostPosted: Sat Apr 15, 2006 11:55 am     Reply with quote
Most likely yes. What GSM MODEM?

It appears that the Millenium already has a level shifter on the board.

John
UU
Guest
PostPosted: Sat Apr 15, 2006 12:14 pm     Reply with quote
its an Enfora sa-gl, ive written code but it wont respond to anything i send to it from the pic, the millenium board uses the max202, ive measured the voltages they are -ve coming out from millenium board is this the way it should be, any more advice? thanks
jecottrell



Joined: 16 Jan 2005
Posts: 559
Location: Tucson, AZ

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PostPosted: Sat Apr 15, 2006 11:51 pm     Reply with quote
Use the following approach to trouble-shooting:

Try the MODEM with a PC and a terminal program similar to Hyperterminal. Does it work? (You need to know whether the MODEM will respond to any comms presented to it.)

Try the Millenium with a PC in the similar manner. Does it work? (You need to know whether the Millenium is actually producing any serial comms.)

Determine the configuration of the Millenium. Is the pinout on the DB9 configured as a DTE or DCE? If you don't understand the difference, then Google the terms and read up on them. (This will tell you whether you can use a straight through serial cable or a null MODEM cable.)

Another possibility is that the MODEM maybe configured for flow control. Read up on the MODEM and learn about the flow control options available on it and how to disable them.

John
UU
Guest
PostPosted: Sun Apr 16, 2006 2:55 am     Reply with quote
the modem is working on hyperterminal, and the millenium board is putting the right commands to hyperterminal its when the two are connected nothing happens i have a debugging prgram written to check the comms. ive made my own leads so that should be ok.

i am using the 3 wire version i took your advice and check with the company to disable the cts and all that, great help just about to try it out now, thanks very much for your help, very very much appreciated(hopefully it works now!!)
UU
Guest
PostPosted: Sun Apr 16, 2006 5:20 am     Reply with quote
it still doesnt work will i have to tie the RTS to the CTS, because the commands are not working
Mark



Joined: 07 Sep 2003
Posts: 2838
Location: Atlanta, GA

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PostPosted: Sun Apr 16, 2006 8:29 am     Reply with quote
If you are using the same cable to test
modem to PC
PIC to PC

then you will need a crossover cable (Null Modem) for
PIC to modem
UU
Guest
PostPosted: Sun Apr 16, 2006 9:02 am     Reply with quote
the problem lies with the PIC and modem communicating with each other, i am using the 3 wire version from the pic to the modem, the other cabling is ok.
jecottrell



Joined: 16 Jan 2005
Posts: 559
Location: Tucson, AZ

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PostPosted: Sun Apr 16, 2006 9:03 am     Reply with quote
Quote:
ive made my own leads so that should be ok.


Don't assume anything. Provide the pinout for the cables. Mark provides good information about whether a Null MODEM cable is required. Have you tried a Null MODEM cable?

Find a terminal program that will allow you to manually assert/de-assert RTS/CTS, etc. That could help in your debugging.

One thing that will help you get much more support from the experts on this forum is to make the effort to provide detailed information about your problem. Tidbits here and there only show that your not quite willing to spend the time to explain your problem. If your not willing to take the time to explain your problem, why should anyone take the time to solve your problem? A detailed explanation with cable pinouts, progress so far, program listings, compiler version, PIC part number, etc., can most times lead to the solution in one quick response from the pros.

(If you can get the MODEM and PC communicating with 'No Flow Control' set, then RTS and CTS are not a factor... NULL MODEM, NULL MODEM, NULL MODEM.......)

John
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