The original schema looks like this.
DTR ---------------------
GND -------------------- schottky diods, resistance and zener diods.
RXD ---------------------
TXD ---------------------
But if you are going to replace DTR with Vcc, I think you should add an
extra resistance just after Vcc.
Otherwise you might break your router if you short Vcc with GND. (+ there
will be some mA through the 3.9V zener which requires the resistance to
avoid short-circuit).
Vcc ----100ohm--------
GND -------------------- + original schema..
RXD ---------------------
TXD ---------------------
I don't think you wrote this in your reply. Does anyone else agree with
this?
/Christian
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] On Behalf Of suman
sarkar
Sent: den 13 september 2007 02:28
To: [email protected]
Subject: [Owfs-developers] Re :Re: Re :Re: Re :Re: MIPS vs MIPSEL in OWFS
OK, Christian ... first of all, thanks for your valuable input.
If I understand it correctly, only 4 pins (2,3,4,5) of standard DB-9 are
used to build an equivalent DS9097 circuit for 1-wire chips, of which DTR
(pin 4) connects to 1-wire Data (probably DQ for Maxim 1-wire chip), and RXD
(pin 2) connects to 1-wire GND (probably P- for Maxim 1-wire chip).
So, with those diodes and resistors in the picture (protection circuit for
the 1-wire chip), I've decided to build my own little circuit for 4-pin for
my board (and not using off-the-shelf 9-pin DS9097).
Conceptually it should work (help me if I am missing anything): DTR (of
DB9) is equivalent to Vcc (my board), RX and TX (of DB9) are equivalent to
TX and RX (my board), respectively, and GND to GND, of course with an
equivalent protection circuit, as shown in the picture.
With this (1-wire chip with my own circuit for 4-pin serial above, which I
presume will be equivalent to DS9097), I guess owfs would be able to see and
mount the /dev/ttyS0, and would NOT complain: "Could not detect DS9097".
Any input from you will be useful before I jump into it.
Another question: what about the other pins of DB9 as shown in the picture?
Are they left open, especially handshaking pins like RTS/CTS (pin 7/8)?
Thanks.
----
On Wed, 12 Sep 2007 20:16:55 +0200 [email protected]
wrote
Shouldn't you be able to use Maxim's reference
design of a passive 9097 adapter?
DTR is there to supply 1-wire bus with power since it's
high when serial-port is opened. This could be replaced with Vcc I think.
Perhaps
an extra 100ohm (just after Vcc) to protect it from short-circuit would
be good too. The DTR pin is probably short-protected on all
serial-interfaces,
but Vcc on your board is probably not.
Look at the drawing at:
http://owfs.sourceforge.net/adapters.html#Serial
Picture: http://owfs.sourceforge.net/adapters/adapter.gif
/Christian
From:
[EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] On Behalf Of suman
sarkar
Sent: den 12 september 2007 01:59
To: [email protected]
Subject: [Owfs-developers] Re :Re: Re :Re: MIPS vs MIPSEL in OWFS
Hi
Christian,
Here are some clarifications re: Meraki AP's serial interface.
This interface is NOT a regular 9-pin interface (DB9) as you see in
WRT54G. It has only 4 pins: Vcc, Tx, Rx, and GND.
OWFS can only support DS9097 serial adapter, I presume, which has a
regular 9-pin serial configuration.
So, any Maxim sensor chip (which is DS2781K in our case), with DS9097
serial adapter CAN NOT be directly fed to the AP's 4-pin interface. It needs
some tweaking, I guess.
Any suggestion regarding how to make it compatible with a 4-pin
interface?
Thanks.
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