Hello,

sorry for this - i think silly - question, but can anybody tell me
wether I need to put pull-up-resistors to the UART outputs RXD, RTS, DTR?

I want to interface a GSM modem via one UART of my MSP430F149, and
concerning the manufacturer of the modem, these signals aren't
internally pulled-up and "... they MAY be pulled-up with an 47k
resistor...".

Now I'm confused... .

Thank you for your suggestions!

regards
Christian

----- Original Message ----- 
From: "Christian Schulz" <junk2005@junk...>
To: <msp430@msp4...>
Sent: Thursday, June 02, 2005 11:15 AM
Subject: [msp430] UART ---> pullups needed?


> Hello,
> 
> sorry for this - i think silly - question, but can anybody tell me
> wether I need to put pull-up-resistors to the UART outputs RXD, RTS, DTR?
> 
> I want to interface a GSM modem via one UART of my MSP430F149, and
> concerning the manufacturer of the modem, these signals aren't
> internally pulled-up and "... they MAY be pulled-up with an 47k
> resistor..."

Most Maxim RS-232 driver chips have pull-ups.

Leon

--- In msp430@msp4..., "Leon Heller" <leon.heller@d...>
wrote:

> 
> Most Maxim RS-232 driver chips have pull-ups.
> 
> Leon

Hello Leon,

I forgot to mention: MSP and GSM-Modem will be together on a PCB, so I
don't need a levelshifter... . Currently the UART signals are
connected straight forward to the modem, without any resistors in/at
the track.

Christian

Christian,
You wont need pull-ups if you keep those lines drived continuosly. They
mention the need for external pull-ups in case you want to keep one or more
input signals open.
Mind that the active state for RS232 signals in the device is zero. So, when
you want to turn RTS line on you have to set this signal to zero (that would
be an ideal +12V level after a level shifter).
You could also think to use pull-downs to keep some lines allways active.
If your MSP430 may fall in a state where the output pins may become inputs,
while GSM is still working, they will float and may be seen by GSM as
data/control comming from MSP and you will have unespected results. If it is
the case you must use pull-ups to ensure those lines will stay in a known
state.
-Augusto


-----Original Message-----
From: msp430@msp4... [HYPERLINK
"mailto:msp430@msp4..."mailto:msp430@msp4...] On Behalf Of
Christian Schulz
Sent: Thursday, June 02, 2005 7:46 AM
To: msp430@msp4...
Subject: [msp430] Re: UART ---> pullups needed?


--- In msp430@msp4..., "Leon Heller" <leon.heller@d...> wrote:

>
> Most Maxim RS-232 driver chips have pull-ups.
>
> Leon

Hello Leon,

I forgot to mention: MSP and GSM-Modem will be together on a PCB, so I
don't
need a levelshifter... . Currently the UART signals are connected straight
forward to the modem, without any resistors in/at the track.

Christian





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