Re: DS2480B based adapter
George M. Zouganelis <gzoug <at> aueb.gr>
2007-02-01 15:57:41 GMT
Jan Kandziora wrote on 1/2/2007 08:20:
> Am Donnerstag, 1. Februar 2007 00:39 schrieb George M. Zouganelis:
>> Simon Natterer wrote on 1/2/2007 01:16:
>>> George M. Zouganelis wrote:
>>>> Today I built a DS2480 serial adapter (schematic attached) after
>>>> failing to work with
>>>> a orginal Elektor schematic (wich had no RS232 level Driver)(Issue
>>>> Apr/2004 By Luc Lemmens)
>>> I have almost the same schematic, but with a MAX232 and there I have to
>>> tie the POL pin to +5V (VDD). I don't know what is the difference of
>>> your ADM232.
>> Arghhhh!!!! ^^^^^^^^^^^^^^^^^
>>
>> Remind me to pay you a beer! :D
>>
> In the DS2480 datasheet, the following is stated:
>
> 6 POL RXD/TXD Polarity Select. RXD/TXD polarity select; tied to GND for RS232
> (12V or 5V) connection; tied to VDD for direct connection to UART chip.
>
> Sorry I lead to certain misconception with the eagle library you used (I
> think). There I've written:
>
> The RxD and TxD lines are operated at 0V/5V. The POL pin selects the RxD and
> TxD "polarity", that means straight-through or inverted. If POL is connected
> to GND, RxD and TxD behave properly for connection to inverted RS232 drivers,
> like the MC1488/1489 or MAX23x chips. If POL is connected to Vdd, RxD and TxD
> behave properly for direct connection to a 0V/5V UART chip.
>
> So the POL pin should be connected to GND if a simple
> diode/transistor/resistor network is is used as the RS232 "interface", like
> the Elektor schematic presumably does. If inverted drivers are used in the
> peripheral, they are used on *both* sides (computer and peripheral), so the
> inversion is gone and POL need to be connected to Vdd.
>
I had caressly left the POL to GND, extending the Elektor schematic :(
MAX232, translates the -12V for '1' and +12V for '0' to +5v for '1'
and 0V for 0 (MPU/TTL compatible), so on the DS2480 side, -12V has
become TTL logic high (+5V) and +12V has become TTL logic 0 (0V).
Now, it sounds clear to me that POL should be connected to Vdd when
dealing with TTL logic inputs (+5V for logic '1') or GND if we are
conneted to RS232 protocol voltages (-5V or -12V for logic 1).
If this is correct, that's what I would like to read on DS2480 specs. Unless I'm
not so familiar with English reading, I find the 11a,b,c figures a bit confusing
concerning the role of UART/uC. I can only be helped reading Figure titles (DIRECT, +/-5V, +/-12V)
> Hmmm. Maybe I should update the library. Could anyone of the native english
> speakers here come up with an unambiguous text?
>
btw, do you know where I can find a good walkthrough tutorial on editing
library components for Eagle (Schematic and PCB)? I need to modify some components
(mainly resizing/relocating their PADs)
> Hmmm. Maybe I should update the library. Could anyone of the native english
> speakers here come up with an unambiguous text?
>
> Kind regards
>
> Jan
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