I'd expect an inverter to explode. The RS-232 is going to swing negative
(below VDD), which will kill most CMOS inverters. If you only have a single
voltage (like +5), you can use RS-232 level converters from companies like
Maxim.
One trick is to use a pair of RS-485 transceivers. They are generally
cheaper than an RS-232 voltage converter and smaller (no CAP required).
Using two, you can do RS-422, RS-485, (both current-diff.) and RS-232
(voltage level).
Really down and dirty, you can use caps and transistors and steal the
required 12V from the handshaking lines from the other end of the connection
(ie, the Palm). I would probably avoid this since the Palm itself is using
a fairly low voltage converter.
-jjf
-----Original Message-----
From: Ben Hamby [mailto:[EMAIL PROTECTED]]
Sent: Tuesday, July 25, 2000 12:23 PM
To: Palm Developer Forum
Subject: RE: Serial Communications
The Tx and Rx in a RS-232 do indeed act much like I/O for a UART, but they
are generally speaking the opposite (at least from my other
experience)....ie. the generic UART defaults low, asserts high, the RS-232
defaults high, asserts low.....essentially my output is the exact opposite
of what i need/expected from an RS-232, the start bit goes high, instead of
low, and the 0's are high while the 1's are low....i'm considering just
throwing an inverter in between, but that could get a little messy for
now...
thanks,
ben
At 10:05 AM 7/25/2000 -0700, you wrote:
>The TX and RX of RS-232 is essentially UART output (UART -> Voltage
>Converter -> connector, matches standard). Also, remember that RS-232 uses
>+/- 12V (nominal) levels, so you will need conditioning before connecting
to
>a PIC.
>
>Good Luck,
>-jjf
>
>-----Original Message-----
>From: Ben Hamby [mailto:[EMAIL PROTECTED]]
>Sent: Tuesday, July 25, 2000 9:36 AM
>To: Palm Developer Forum
>Subject: RE: Serial Communications
>
>
>I see what you mean now, as far as the differences between the SPI and the
>common UART(ie. 16550)...However, isn't the RS232 supposed to have similar
>output to the SPI? Ie. defaults high, assertions are low....and I thought
>the Palm had an RS232...does it have both and defaults to using the 16550
>protocol? Or am I out in right field without a glove....
>
>Thanks,
>Ben
>
>At 03:14 PM 7/24/2000 -0700, you wrote:
> >The SPI is quite a bit different from a standard async serial port. You
>can
> >implement an async serial port in software on most PICs. I did one a
long
> >time ago on a PIC16C50 derivative and it worked pretty well.
> >
> >If you go to www.microchip.com and select Application Notes, a note on
> >implementing an async port will be one of the first ones listed.
> >
> >Good Luck,
> >-jjf
> >
> >-----Original Message-----
> >From: Ben Hamby [mailto:[EMAIL PROTECTED]]
> >Sent: Monday, July 24, 2000 12:43 PM
> >To: Palm Developer Forum
> >Subject: Serial Communications
> >
> >
> >Hello,
> >
> >I'm doing serial communication between my Palm and another device that
uses
> >a PIC processor. Just had a few questions I was wondering if anyone
could
> >answer about the format of the output more than how to program it. (all
of
> >this is from the Tx line) Right now, I just send some information out of
> >the SerSend command and it sends fine, but I was wondering if the Palm by
> >default includes a 1 bit start bit. Currently, it seems like the line
> >defaults to Low(0) and then sends a 1 bit High(1) out of the Tx before it
> >sends a byte. Is this how normal serial communication is performed? I
> >thought the serial communication went in a similar style to the SPI,
where
> >it defaults to a High and then sends a 1 bit Low before sending the
> >information? Is my information incorrect? If it is, and that is how
normal
> >serial communication is performed, does anyone have any suggestions to
get
> >it to work with the SPI?
> >
> >Thanks,
> >Ben
> >
> >
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> >
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>
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