I/O Cards

jthornton

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Jul 2002
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Is there any standard practice for the location of I/O cards?

SCL500 system

Do you put the input cards first or output cards first or does it make any difference?


TIA
John
 
Position of input and output cards make no difference, the only thing to remember is that if you are using expansion racks then you can usually minimise the size of your power supplies by splitting up the output cards between the racks. (output cards usually draw more power from the backplane). There are some cards that cannot be mounted in an expansion rack (I can't remember them all but I think the remote IO scanner and Devicenet scanner need to go in the base rack) I can also vaguely remember that some style of card needs to go in slot 1 (next to the processor) but I could be wrong on this last one. I'm sure (and hope) Ken will correct me in this if I am wrong. Regards Alan Case
 
The SLC-500 controllers are fairly simple in this regard; there are no restrictions on module order except for the CPU, which must occupy the left-most slot.

This is true for all 30 possible slots (if chassis are linked via backplane extension cables) of an SLC-500 system. There are restrictions on what kind of modules can be placed in chassis that are scanned by some sort of Remote I/O network, but that's outside the scope of this question.

The guiding rule for module mix in an SLC-500 chassis is, as Alan mentioned, the amount of power available in the chassis. Analog cards use up more power than discrete ones, and outputs more than inputs.

I typically group inputs first, outputs next, and analog cards last. This is strictly a habit; there's no reason to do so other than to segregate the voltages I have present in the cable trays underneath the cards.

PLC-5 users know well the tricks and rules of 1-slot, 2-slot, and 1/2-slot, or even Complementary addressing that the old 1771 system used. A headache at it's mildest, this is one of the reasons for the the simplified design of the SLC-500 backplane. Every module in the SLC chassis is addressed principally by it's physical location.

The SLC-500 Modular Controllers User Manual is close at hand on my desk:

http://www.ab.com/manuals/cp/1747-um011c-en-p.pdf
 
quote:
--------------------------------------------------------------------------------
Originally posted by Ken Roach
PLC-5 users know well the tricks and rules of 1-slot, 2-slot, and 1/2-slot, or even Complementary addressing that the old 1771 system used. A headache at it's mildest, this is one of the reasons for the the simplified design of the SLC-500 backplane. Every module in the SLC chassis is addressed principally by it's physical location.
--------------------------------------------------------------------------------


When using a scanner module (1747-SN) to communicate to a remote rack, you will need to understanding slot addressing. You can use 2-slot addressing, 1-slot addressing or 1/2-slot addressing. It becomes important due to the way the scanner and adapter handles memory. Typically when using 1-slot addressing, each slot is assigned one word (16 bits) of the 1747-ASB module’s input and output image. If you are using a 4 point analog input card which needs to use 4 words of address space, you will need to either use 1/2 slot addressing and leave the slot beside analog module empty (when using discrete mode), or use 1 slot addressing with block transfer mode.

For more information on slot addressing, refer to your ASB module user manual.

Remote I/O Adapter Module (1747-ASB) http://www.ab.com/manuals/cp/1747613.pdf
Remote I/O Scanner (1747-SN) http://www.ab.com/manuals/cp/174766.pdf
 
Peter's comment is a good one. I usually leave open slots (if they are available) between my discrete I/O modules and my analog modules, in order to get as much physical seperation between my AC and DC level signals, cable routing, etc. If my system has to 'grow' in the future, I expand towards the middle of the rack. If you (or your customer) have 'cosmetic' issues with open slots, some PLC's have blank 'slot fillers' to provide a cleaner looking system.
 
IO Cards

It is healthy to consider installing the Analog I/O cards in the leftmost slots near to the CPU, this will decrease the congenstion of data traveling from the Analog I/O to the CPU and could improve performance, mostly if your PLC is loaded with lots of Digital I/O in the other slots.
 
Sherman4, I've never heard that one before. Would you care to elaborate? My first impression was that you're implying that I/O modules located closer to the CPU get updated more frequently or more reliably than those located further away.
 
It has been along time since I used slicks but, I seem to remember having to place my comms or HS counter or smart cards closest to the CPU then my DC cards then AC cards. Granted I was not restricted by the CPU configuration, it was more of a good practice. I know I received this information from Allen Bradley (I thought it was in the documentation). Again this was good practice and not a restriction.
 
I/O cards

Maybe I was not clear enough, I´ve read that it is peferable to have all analog cards in the first chassis (if you pretend to expand your system), because the transmission time is longer when the processor is scanning the cards if they are remotely located (expansion chassis).
 
Hi,

It's a bit out, but pls help:

I was testing my 1747-ASB for some I/O mapping last week. Today when I tried to power-on my chassis with 1747-ASB inside, the ASB just hang, shows a number '8' on it. Fault LED also on. Tried to take out all cards, but don't help.

Notice there is a small jumper on board, but not labelled. WIll it help me to reset?

Thanks.

Regards,
CK chew
 

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