Is it we put lower resistor for pull up's the data signal on transmition would be more stable? Because enough current to flow through the cable?
On the receiving end...how can i terminate the reflections?
Hello Help,
Yes, a lower resistance causes more current to flow and thereby charges and discharges the (line) capacities faster, so that the rising and falling edges of the datawaveform stay steep enough, otherwise you get timeshift problems. That is one reason, the other one is to prevent reflections, and they become less in amplitude if your resistance (on both ends of the line) get nearer the characteristics of the cable.
Your cable will have a characteristic resistance between 100 and 200 ohms I think, so your 10k should go down as far as possible to that value. But the driver must be able to sink that low resistance (from the pull-up) to ground, otherwise you dont cross the threshold of the detection on the receiving end. So you must find a compromise.
I would try 1k as pullup on the transmitter and 1k (to +vb) on the receiving end.
See what happens to your throughput (speed).
I'll see what the 573 and the 07 can drive and take a look on that interfacebus site.
Good luck, Yoda.
Posted on: December 15, 2007, 11:04:41 23:04 - Automerged
.how can i terminate the reflections?
I had do some study on LVDS http://www.interfacebus.com/Design_Connector_LVDS.html
Hello Help,
I look'd at the interfacebus site, the LVDS interface is not wat you want, it is a balanced line design, like RS485 or 422.
I also saw that the HC573 is a good choice (you made earlier), it can sink 25 ma, so your termination resistors may go as low as 200 ohms.
So you may change your pull-up's to 470 ohm on the 573 side, and also 470 ohms on the receiver side (in parallel they deliver less than 25 ma then).
Because you want such a low data rate (1 second? per byte) you should not worry too much for the receiver side (1 to 10 K) will still work there.
Only if you want faster throughput of data the reflections on the line must be taken care of. Also decouple your powerline at the driverpoint with 10uF or more, because 8 or 16 x a zero in the data, means around 300mA current. Take care that your oVolt or ground wire can supply that current (extra wire from driver to psu connection, and the elco on the 573 supply pins).
A secure way to deliver data this way is to send a separate strobe signal to the receiver, a short time (1 or more milliseconds) after the data is enabled, (and the lines came to rest, (reflection has gone then)) if you do that, the whole resistor termination story can be forgotten, important than remains: a low impedance circuit is less sensitive to external inductions then a high imp. one.
Good luck again.
