Problems with Flex i/o


Thread Starter

Marco A. Zaragoza

I´ve experienced some troubles trying to connect a new ASB module. I have already two scanners on a SLC 5/04, the one that i´m using has another two ASBs connected to it. The problem its with the third one, this only have one ie8 module, i´have configured it in compact mode, and it works o.k. but the other ones, i mean the other two ASB looks like running slowly than before.

I hadn´t wired the terminal resistors, could this be the reason, Plus there are two ASBs connected in one cable line and were configured like logical rack 0 and 1, but the one that I want to connect its in another cable line i mean i´ve
connected another cable to the scanner appart of the another one that is attach to the scanner and the other two modules....

Whoa, Marco, back up. This is simple to fix.

Any network's I/O response time will increase when you add traffic to it.
RIO is no different.

If you've added another 1794-ASB adapter to the scanlist of a 1747-SN, the discrete I/O scan will be slightly slower (you're scanning 3 adapters now
instead of 2).

Because you'll also be sending block transfers to an analog input module (the 1794-IE8), other block transfers will have to wait their turn, slowing down the total throughput of analog data. If you're having trouble programming the block transfers, a number of knowledgebase documents from the A-B support site may help.

Although you can "sometimes" get RIO networks to function without them, termination resistors are always required for RIO.

You should put termination resistors across the blue and white wires at the "third ASB" and at the "second ASB", resulting in a RIO daisy-chain that goes like this:

(T) ASB --- SN ---- ASB --- ASB (T)

Use 150 ohm terminators for 57.6 kb/s or 115.2 kb/2 data rates, and 82 ohms for 230.4 kb/s data rate. Follow the manual's recommendations about the shield drain at the 1747-SN.

Good luck,

Ken Roach
A-B Seattle

Michael R. Batchelor

Get the AB datasheets, and connect the modules like the datasheets say. daisy chain the blue hose correctly, and put the resistors on either end. While that's always necessary, that's the very first troubleshoot step. If you're outside the box, get back in the box before looking any further.