DF1 Devices on DH-485

How can I put 4 devices communicating on RS-232 DF1 Protocal on the DH-485 Network. I Believe 1 is easy with a SLC 50/3 But I can't find a way to do 4.<br>
Help !!!<br>
 
S

Stephenson, John E.

You cannot use RS-232 for multi-drop, it is only for point-to-point. If all 4 devices support DH-485 ( which is Data Highway on RS-485 which is
multi-drop ) then use that. Another option is to use serial communications modules in your PLC rack and use one RS-232 port for one device. Or, if the devices are addressable and can be set up to retransmit what they receive you might be able to daisy chain them together (ie. the TX of the first to the RX of the Second. The TX of the second to the RX of the third and so on until you tie the final TX to the first RX ).

good luck
 
It is easy but expensive. You need four 1770-KF3 "modems" or four 1747-KE cards. These interface from DH-485 to DF1. The KE cards are a lot
cheaper, if you have four slots available.

Bill Sturm
 
E

Eric M. Klintworth

Every node on a DH-485 network must be talking DH-485 protocol. Many A-B devices, such as SLC-5/03 and up and most MicroLogix can talk DF1 or
DH-485 protocol out their RS-232 port (Channel 0). Only a dumb external device (1747-NET-AIC) is required between the port and the DH-485
network for electrical isolation and conditioning.

For devices that can only talk DF1 protocol, use a 1747-KE (SLC slot mount) or 1770-KF3 (freestanding) interface module. The interface
modules exist as a node on the DH-485 network and convert between DF1 and DH-485 protocols. The most common use is connecting a dial-up modem
to a DH-485 network.

If you have further questions, e-mail the list, or me directly, with the details about what those 4 devices are and the distance between them.

Good luck,
Eric M. Klintworth, P.E.
Columbus, Ohio
-----------------------------
 
If all of the devices natively support DF1 then it is easy. You need the 1761-NET-AIC device from A-B. This device can bridge from DH485 to RS-232.

Let me know if there is anything else I can help with.

Bradley G. Hite
Vice-President
Intertech Inc.
mailto:[email protected]
ICQ# is 38746036
http://www.myplc.com
Teaching Practical Skills For a Technological World
 
E

Eric M. Klintworth

[email protected] wrote:
> > How can I put 4 devices communicating on RS-232 DF1 Protocal
> > on the DH-485 Network. I Believe 1 is easy with a SLC 50/3 But I can't
> > find a way to do 4.
> > Help !!!

Bradley G. Hite replied:
> If all of the devices natively support DF1 then it is easy. You need the
> 1761-NET-AIC device from A-B. This device can bridge from DH485 to RS-232.
>
<snip>
Eric M. Klintworth writes:
No, sorry, the 1761-NET-AIC is only an electrical converter/isolator. An RS-232 device attached to a DH-485 network via a 1761-NET-AIC must be
talking DH485 protocol. If the RS-232 device can only talk DF1 protocol, a 1747-KE or 1770-KF3 must be used to do the protocol conversion.

Eric M. Klintworth, P.E.
Columbus, Ohio
 
M
The 1747-KE & 1770-KF3 are DH485/DF1 Interface Modules, so not suitable for the SLC5/04 directly. You could however still use one 1747-KE or 1770-KF3 module with a DH485 network running to each SLC5/04, as long as each one has
a 1747-AIC module & 1747-PIC Interface Converter hooked up to the RS 232 Channel 0 port, and configured for DH485. Its a bit long-winded and still somewhat expensive. Rockwell Automation will be able to help you further. Also the 1747-KE
module does not support slave-to-slave transfers.

Regards, Mike Lynch
 
D

Darold Woodward

Seems to me that you could logically use one of the 4 as a DF1 master and collect the data from the other 3. (This really depends on the demands of your application.) This could be accomplished by using EIA-485 and exploiting the addressing in the DF1 protocol. Next you would make the concentrated, aggregated data available to the DH-485 network by connecting only the DF1 master device to the DH-485 with a KE card.

Darold Woodward PE
SEL Inc.
[email protected]
 
T

Trevor Ousey

We have a system running 4x dc servo drives which are controlled via RS232 from an AB slc5/04 on its serial port. The drives are manufactured by JVL in Denmark, and communication is both ways. To address a command to a drive, the address number is prefixed to the command. As far as I can tell it is standard RS232, there are no convertors in line, and Channel 0 is configured
as user running ASCII.

Regards,
Trevor Ousey
 
N

Norbert Koot

Your drives must be non-standard RS-232. If they were standard, then the drive's Transmit Data pin would be holding a negative DC voltage while idle. If the TD pin is shared and one of the drives starts to transmit, it will apply an alternating positive and negative voltage. The positive will tend to cancel the negative from the other drive(s) and the voltage will not rise. I suspect that these drives are designed
with a blocking diode on the TD pin that only passes positive voltages, so that they can be multidropped. I have seen this technique used elsewhere. With such a modification, the channel will be less tolerant of noise, and in addition may not be able to power those "self powered" modems that are on the market.

Norbert Koot


: From: "Trevor Ousey" <[email protected]>
:
: We have a system running 4x dc servo drives which are controlled via RS232
: from an AB slc5/04 on its serial port. The drives are manufactured by JVL in
: Denmark, and communication is both ways. To address a command to a drive,
: the address number is prefixed to the command. As far as I can tell it is
: standard RS232, there are no convertors in line, and Channel 0 is configured
: as user running ASCII.
...<clip>
 
L
Just for reference, several RS-232 chip makers have products with tri-state transmit pins much like RS-485. I've seen a number of "flow computers" use this to allow a crude multi-drop sharing of a serial RS-232 printer (they assume only 1 operates at a time - ie: like parallel pipelines at one loading point).

However, the IEA/RS-232 standard has no spec as to how such a high-impedance RS-232 transmitter would appear or load the line, so these are basically single vendor solutions unless trial-n-error proves otherwise.

Best Regards

Lynn August Linse, Senior Product Application Engineer
15353 Barranca Parkway, Lantronix Inc, Irvine CA 92618
[email protected] www.lantronix.com
Tel: (949)450-7272 Fax: (949)453-7132
 
Top