| Author |
Message |
Richard
Guest
|
 Posted:
Wed Nov 16, 2005 8:41 am Post subject:
RS485 Chip |
|
|
I have a 75176 RS485 Transceiver chip here. Looking at the application
notes, it seems pretty straight forward to hook up, however I'm wondering.
Should I add a Jumper and a termination 120 ohm Resistor Between A and B?
Should I install any pull ups or Pull downs on the 485 data signal lines?
Does A pull down and B pulls Up?
Just wanting to do this 1 time. I will be using it strickly in half duplex
(For ModBus Mode).
Thanks for any pointers.
Richard
----== Posted via Newsfeeds.Com - Unlimited-Unrestricted-Secure Usenet News==----
http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups
----= East and West-Coast Server Farms - Total Privacy via Encryption =----
|
|
| Back to top |
|
 |
Dan Hollands
Guest
|
| Posted:
Thu Nov 17, 2005 5:35 pm Post subject:
Re: RS485 Chip |
|
|
Don't add any pull up or pull down
There needs to be a termination resistor at the end of the cable run.
Dan
--
Dan Hollands
1120 S Creek Dr
Webster NY 14580
585-872-2606
QuickScore@USSailing.net
www.QuickScoreRace.com
"Richard" <rwskinnerATawesomenetDOTnet> wrote in message
news:1132108965_15513@spool6-east.superfeed.net...
| Quote: | I have a 75176 RS485 Transceiver chip here. Looking at the application
notes, it seems pretty straight forward to hook up, however I'm wondering.
Should I add a Jumper and a termination 120 ohm Resistor Between A and B?
Should I install any pull ups or Pull downs on the 485 data signal lines?
Does A pull down and B pulls Up?
Just wanting to do this 1 time. I will be using it strickly in half
duplex (For ModBus Mode).
Thanks for any pointers.
Richard
----== Posted via Newsfeeds.Com - Unlimited-Unrestricted-Secure Usenet
News==----
http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+
Newsgroups
----= East and West-Coast Server Farms - Total Privacy via Encryption
=---- |
|
|
| Back to top |
|
|
James T. White
Guest
|
| Posted:
Fri Nov 18, 2005 1:35 am Post subject:
Re: RS485 Chip |
|
|
"Richard" <rwskinnerATawesomenetDOTnet> wrote in message
news:1132108965_15513@spool6-east.superfeed.net...
| Quote: | I have a 75176 RS485 Transceiver chip here. Looking at the application
notes, it seems pretty straight forward to hook up, however I'm wondering.
Should I add a Jumper and a termination 120 ohm Resistor Between A and B?
Should I install any pull ups or Pull downs on the 485 data signal lines?
Does A pull down and B pulls Up?
Just wanting to do this 1 time. I will be using it strickly in half duplex
(For ModBus Mode).
|
Check the TI, National, Maxim and Linear Technology websites for application
notes related to RS485, termination and failsafe.
--
James T. White
|
|
| Back to top |
|
|
tlbs
Guest
|
| Posted:
Fri Nov 18, 2005 11:39 pm Post subject:
Re: RS485 Chip |
|
|
Richard wrote:
| Quote: | I have a 75176 RS485 Transceiver chip here. Looking at the application
notes, it seems pretty straight forward to hook up, however I'm wondering.
Should I add a Jumper and a termination 120 ohm Resistor Between A and B?
Should I install any pull ups or Pull downs on the 485 data signal lines?
Does A pull down and B pulls Up?
Just wanting to do this 1 time. I will be using it strickly in half duplex
(For ModBus Mode).
|
You need to terminate the transmission line (across A and B) with the
characteristic impedance of the twisted pair transmission line you are
using. If that characteristic impedance is unknown, any value from 98
to 125 Ohms will usually do the trick.
The only reason to use pullup and/or pulldown resistors is for ESD
protection of the 75176. Values between 10 kOhms and 50 kOhms will add
protection to the RS485 receiver. You could also use switching diodes
or MOV devices. If you pullUP the non-inverted input, and pullDOWN the
inverted input, then the fail-safe value of the logic output will be
"TRUE". |
|
| Back to top |
|
|
Richard
Guest
|
| Posted:
Sat Nov 19, 2005 12:35 am Post subject:
Re: RS485 Chip |
|
|
Thanks for all the advice. I noticed while looking thru many schematics
that each person seems to implement the 485 chips in many different ways. I
think I will put the termination, pull up, and pull downs all on there being
jumper selectable and that way I can have it either way.
Richard
"tlbs" <tlbs101@excite.com> wrote in message
news:1132335586.439370.203560@g49g2000cwa.googlegroups.com...
| Quote: |
Richard wrote:
I have a 75176 RS485 Transceiver chip here. Looking at the application
notes, it seems pretty straight forward to hook up, however I'm
wondering.
Should I add a Jumper and a termination 120 ohm Resistor Between A and
B?
Should I install any pull ups or Pull downs on the 485 data signal lines?
Does A pull down and B pulls Up?
Just wanting to do this 1 time. I will be using it strickly in half
duplex
(For ModBus Mode).
You need to terminate the transmission line (across A and B) with the
characteristic impedance of the twisted pair transmission line you are
using. If that characteristic impedance is unknown, any value from 98
to 125 Ohms will usually do the trick.
The only reason to use pullup and/or pulldown resistors is for ESD
protection of the 75176. Values between 10 kOhms and 50 kOhms will add
protection to the RS485 receiver. You could also use switching diodes
or MOV devices. If you pullUP the non-inverted input, and pullDOWN the
inverted input, then the fail-safe value of the logic output will be
"TRUE".
|
----== Posted via Newsfeeds.Com - Unlimited-Unrestricted-Secure Usenet News==----
http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups
----= East and West-Coast Server Farms - Total Privacy via Encryption =---- |
|
| Back to top |
|
|
|
|
|
|
FAQ
Memberlist
Register
Profile
Log in to check your private messages
Log in