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aleksazr@gmail.com
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      06-14-2012, 07:14 PM
I need to output 3 signals and input 2, (all 1 MHz)
over a 5m cable in a relatively noisy environment.
All channels are independent.

Currently, I'm using rs-422 and a total of 10 wires.

How can I bring the wire number to a minimum?


I don't have any experience with serdes chips,
but the things I don't like are: (example, TI SN65LV1021)
- even the smallest chip is too big (has 28 pins),
- uses LVDS which I don't think works best in noisy environments,
- requires SYNC1-2 operation (I think).
 
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Boudewijn Dijkstra
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      06-15-2012, 10:50 AM
Op Thu, 14 Jun 2012 21:14:23 +0200 schreef <(E-Mail Removed)>:
> I need to output 3 signals and input 2, (all 1 MHz)
> over a 5m cable in a relatively noisy environment.
> All channels are independent.
>
> Currently, I'm using rs-422 and a total of 10 wires.
>
> How can I bring the wire number to a minimum?


* Orthogonal frequency-division multiplexing.
* Wireless.

> I don't have any experience with serdes chips,
> but the things I don't like are: (example, TI SN65LV1021)
> - even the smallest chip is too big (has 28 pins),
> - uses LVDS which I don't think works best in noisy environments,


Excuse me? From Wikipedia:
"the tightly coupled transmission wires will reduce susceptibility to
electromagnetic noise interference because the noise will equally affect
each wire and appear as a common-mode noise"

> - requires SYNC1-2 operation (I think).



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aleksazr@gmail.com
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      06-15-2012, 11:14 AM
On Friday, June 15, 2012 12:50:17 PM UTC+2, Boudewijn Dijkstra wrote:
> Excuse me?


Over a 5m cable?
 
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Yellow
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      06-15-2012, 12:21 PM
On 14/06/2012 20:14, (E-Mail Removed) wrote:
> I need to output 3 signals and input 2, (all 1 MHz)
> over a 5m cable in a relatively noisy environment.
> All channels are independent.
>
> Currently, I'm using rs-422 and a total of 10 wires.
>
> How can I bring the wire number to a minimum?
>
>
> I don't have any experience with serdes chips,
> but the things I don't like are: (example, TI SN65LV1021)
> - even the smallest chip is too big (has 28 pins),
> - uses LVDS which I don't think works best in noisy environments,
> - requires SYNC1-2 operation (I think).


2 or 3 plastic fibres ( TOSLink or some such ) and serialised data/clock?

LVDS itself should work ok in a noisy environment, but be careful of the
common-mode maximum voltages that the transceivers can withstand. It
does sound a bit of overkill for what you are trying to do.




 
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aleksazr@gmail.com
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      06-15-2012, 02:31 PM
I was hoping to hear something like:

there is a transceiver chip,
X inputs, X outputs,
2 diff. pins (rs-422),
1 pin for OSC,
VCC and GND.

Two of these chips communicate w/o any intervention,
passing the inputs through one pair of twisted wires
from the first chip to the outputs of the second chip - in first time frame,
then doing the same in the opposite direction in the second time frame.
 
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Tim Wescott
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      06-15-2012, 03:53 PM
On Fri, 15 Jun 2012 07:31:33 -0700, aleksazr wrote:

> I was hoping to hear something like:
>
> there is a transceiver chip,
> X inputs, X outputs,
> 2 diff. pins (rs-422),
> 1 pin for OSC,
> VCC and GND.
>
> Two of these chips communicate w/o any intervention, passing the inputs
> through one pair of twisted wires from the first chip to the outputs of
> the second chip - in first time frame, then doing the same in the
> opposite direction in the second time frame.


They're called FPGAs, but the configuration can be a bit of a chore...

--
My liberal friends think I'm a conservative kook.
My conservative friends think I'm a liberal kook.
Why am I not happy that they have found common ground?

Tim Wescott, Communications, Control, Circuits & Software
http://www.wescottdesign.com
 
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Tim Wescott
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      06-15-2012, 04:02 PM
On Thu, 14 Jun 2012 12:14:23 -0700, aleksazr wrote:

> I need to output 3 signals and input 2, (all 1 MHz) over a 5m cable in a
> relatively noisy environment. All channels are independent.
>
> Currently, I'm using rs-422 and a total of 10 wires.
>
> How can I bring the wire number to a minimum?
>
>
> I don't have any experience with serdes chips, but the things I don't
> like are: (example, TI SN65LV1021) - even the smallest chip is too big
> (has 28 pins), - uses LVDS which I don't think works best in noisy
> environments, - requires SYNC1-2 operation (I think).


Not enough information, sir!

"3 signals and input 2"? Three outputs and two inputs, maybe?

(all 1 MHz)? Do you mean that each one, at top speed, can have a 1MHz
square wave (i.e., a 500ns on-pulse followed by a 500ns off-pulse)? Or
do you mean that each one, at top speed, can have 1 mega-baud data on
it? Or something else?

What is "relatively noisy?" Relative to what?

What is "too big"? Obviously, you feel that 28 pins is too big, but
what's your threshold?

What system are you putting this in to? Are you trying to paste
something onto existing boards with minimal changes? Are you doing a
brand new design? Are you trying to hang this on the outsides of
existing boxes without loosening a screw? If you're doing a new design,
or a significant spin, what sort of communications possibilities are
already on the boards (microcontrollers, FPGA, etc.)?

--
My liberal friends think I'm a conservative kook.
My conservative friends think I'm a liberal kook.
Why am I not happy that they have found common ground?

Tim Wescott, Communications, Control, Circuits & Software
http://www.wescottdesign.com
 
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aleksazr@gmail.com
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      06-15-2012, 06:10 PM
On Friday, June 15, 2012 5:53:50 PM UTC+2, Tim Wescott wrote:
> On Fri, 15 Jun 2012 07:31:33 -0700, aleksazr wrote:
>
> > I was hoping to hear something like:
> >
> > there is a transceiver chip,
> > X inputs, X outputs,
> > 2 diff. pins (rs-422),
> > 1 pin for OSC,
> > VCC and GND.
> >
> > Two of these chips communicate w/o any intervention, passing the inputs
> > through one pair of twisted wires from the first chip to the outputs of
> > the second chip - in first time frame, then doing the same in the
> > opposite direction in the second time frame.

>
> They're called FPGAs, but the configuration can be a bit of a chore...
>
> --
> My liberal friends think I'm a conservative kook.
> My conservative friends think I'm a liberal kook.
> Why am I not happy that they have found common ground?
>
> Tim Wescott, Communications, Control, Circuits & Software
> http://www.wescottdesign.com


Damn, so no-one finds that sort of thing interesting enough to produce it.
 
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aleksazr@gmail.com
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      06-15-2012, 06:34 PM
On Friday, June 15, 2012 6:02:25 PM UTC+2, Tim Wescott wrote:
> On Thu, 14 Jun 2012 12:14:23 -0700, aleksazr wrote:
>
> > I need to output 3 signals and input 2, (all 1 MHz) over a 5m cable in a
> > relatively noisy environment. All channels are independent.
> >
> > Currently, I'm using rs-422 and a total of 10 wires.
> >
> > How can I bring the wire number to a minimum?
> >
> >
> > I don't have any experience with serdes chips, but the things I don't
> > like are: (example, TI SN65LV1021) - even the smallest chip is too big
> > (has 28 pins), - uses LVDS which I don't think works best in noisy
> > environments, - requires SYNC1-2 operation (I think).

>
> Not enough information, sir!
>
> "3 signals and input 2"? Three outputs and two inputs, maybe?


Yes... didn't I mention that in the first post?

>
> (all 1 MHz)? Do you mean that each one, at top speed, can have a 1MHz
> square wave (i.e., a 500ns on-pulse followed by a 500ns off-pulse)? Or
> do you mean that each one, at top speed, can have 1 mega-baud data on
> it? Or something else?


1MHz square wave.

>
> What is "relatively noisy?" Relative to what?
>


Ah, you got me there. Dunno.
It all depends on where the owner will put the final product.

It can be in his house, but also in his garage,
or inside a factory where he cuts steel. (for example)


> What is "too big"? Obviously, you feel that 28 pins is too big, but
> what's your threshold?


When I just see a number, 28 - it looks big. (a DIP pops to my mind)
Having checked the footprint, its only 10*8mm - not that big after all.

But its expensive, Farnell has it at ~10EUR for sender.
Thats about 40 EUR for two-way comm - too much.

>
> What system are you putting this in to? Are you trying to paste
> something onto existing boards with minimal changes? Are you doing a
> brand new design? Are you trying to hang this on the outsides of
> existing boxes without loosening a screw? If you're doing a new design,
> or a significant spin, what sort of communications possibilities are
> already on the boards (microcontrollers, FPGA, etc.)?
>


On one side I'm creating a new design,
and on the other I'm inserting new components.

You did mention FPGAs here and in one other post in this same thread.
Yes, I have a FPGA on the main board.

The slave board doesn't - I could put a CPLD there.
Not sure, though, if the logic will fit inside the CPLD.

Guess I will have to try and see.
 
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Tim Wescott
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      06-15-2012, 09:30 PM
On Fri, 15 Jun 2012 11:34:14 -0700, aleksazr wrote:

> On Friday, June 15, 2012 6:02:25 PM UTC+2, Tim Wescott wrote:
>> On Thu, 14 Jun 2012 12:14:23 -0700, aleksazr wrote:
>>
>> > I need to output 3 signals and input 2, (all 1 MHz) over a 5m cable
>> > in a relatively noisy environment. All channels are independent.
>> >
>> > Currently, I'm using rs-422 and a total of 10 wires.
>> >
>> > How can I bring the wire number to a minimum?
>> >
>> >
>> > I don't have any experience with serdes chips, but the things I don't
>> > like are: (example, TI SN65LV1021) - even the smallest chip is too
>> > big (has 28 pins), - uses LVDS which I don't think works best in
>> > noisy environments, - requires SYNC1-2 operation (I think).

>>
>> Not enough information, sir!
>>
>> "3 signals and input 2"? Three outputs and two inputs, maybe?

>
> Yes... didn't I mention that in the first post?
>
>
>> (all 1 MHz)? Do you mean that each one, at top speed, can have a 1MHz
>> square wave (i.e., a 500ns on-pulse followed by a 500ns off-pulse)? Or
>> do you mean that each one, at top speed, can have 1 mega-baud data on
>> it? Or something else?

>
> 1MHz square wave.
>
>
>> What is "relatively noisy?" Relative to what?
>>
>>

> Ah, you got me there. Dunno.
> It all depends on where the owner will put the final product.
>
> It can be in his house, but also in his garage,
> or inside a factory where he cuts steel. (for example)
>
>
>> What is "too big"? Obviously, you feel that 28 pins is too big, but
>> what's your threshold?

>
> When I just see a number, 28 - it looks big. (a DIP pops to my mind)
> Having checked the footprint, its only 10*8mm - not that big after all.
>
> But its expensive, Farnell has it at ~10EUR for sender.
> Thats about 40 EUR for two-way comm - too much.
>
>
>> What system are you putting this in to? Are you trying to paste
>> something onto existing boards with minimal changes? Are you doing a
>> brand new design? Are you trying to hang this on the outsides of
>> existing boxes without loosening a screw? If you're doing a new
>> design,
>> or a significant spin, what sort of communications possibilities are
>> already on the boards (microcontrollers, FPGA, etc.)?
>>
>>

> On one side I'm creating a new design,
> and on the other I'm inserting new components.
>
> You did mention FPGAs here and in one other post in this same thread.
> Yes, I have a FPGA on the main board.
>
> The slave board doesn't - I could put a CPLD there.
> Not sure, though, if the logic will fit inside the CPLD.
>
> Guess I will have to try and see.


Depending on your latency requirements you may be able to do something
with RS485 an one pair of lines, or RS422 and two pairs. If you could
figure out a solid framing scheme, then cramming the whole thing into a
CPLD may be quite doable.

Some FPGAs come with LVDS drivers -- but as its been ages since I've had
to go shopping for FPGAs, I couldn't tell you exactly where to look
(beyond the Xilinx and Altera web sites).
 
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