Re: [uCsimm] Problems with RTS and CTS in uCsimm

From: Tom Walsh (
Date: Tue Dec 19 2000 - 19:49:43 EST

Asier Goikoetxea Yanci wrote:
> Hello Claudio,
> I don't modified the uCsimm, and I don't need convert CTS and RTS to
> RS232 level signals because the modem that I'm using has TTL level signals,
> so I only need convert RS232 signals to TTL (just RxD and TxD).
> So, what can I do?, Should I convert 0/3.3v signals to 0/5vsignals?
> If uCsimm's output high minimun is 2.4v, and input high maximun is 7v, there
> shouldn't be problems to communicate uCsimm with a modem, no?

Okay, you are on the right track here. You understand the voltage
level problem when interfacing logic, this is good. The DragonBall
processor is "5 volt tolerant", this means that while you can use TTL
signal levels to the chip it is not recommended for production
purposes. The long-term affects of a TTL level signal being applied to
the input pin of the DragonBall will tend to degrade the input
circuitry. Motorola does recommend level shifting to the 3 volt level..
Your choice. Myself? I never ASSume, I level shift the signals.

As to the RTS/CTS, I do not believe that the RS232 driver code for the
serial handler in uClinux implements (or knows how to handle) the
hardware handshake lines. You will probably have to implement the
handshaking yourself in the driver code == OR == you can turn on the
hardware handshake that is implemented within the processor itself.
Read the manual on the DragonBall, it does implemnet a hardware
handshake on those pins, but you have to program the hardware to enable
it. I have verified that the on-board chip hardware does implement a
RTS/CTS handshake.

As you may know, this is what embedded programming is all about, it is
not about installing packages (ala' Windoze), but functionality comes
from your own creativity. The uClinux gives you a basic O/S, the rest
is up to you!



Tom Walsh - WN3L - Embedded Systems Consultant
'', ''
"Windows? No thanks, I have work to do..."
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