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Old November 21st, 2011, 05:27 AM   #1
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SLC500 Multiple Rack addressing

Hi All,
In an SLC500 system, with more than one rack, what is the Rack/Slot/Bit address format? I know that the first slot in a rack is '0' as far as the program is concerned, but what is the physical address with regards to the rack, slot and bit? I have seen many different answers to this. Some say the physical address is for example: the first rack is rack 1 - the first slot is slot 1 and the first bit is bit 1. Others say that the first rack is rack 0 - the first slot is slot 0 and the first bit is bit 0. I have also seen other combinations of this! All very confusing. Could someone shine some light on this for me. Thanks in advance.
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Old November 21st, 2011, 08:22 AM   #2
Sergei Troizky

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There are no racks in SLC addresses, but slots only.
The processor is the leftmost slot0, the rest is numbered in order thorough all existing racks.
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Old November 21st, 2011, 11:47 AM   #3
The Plc Kid
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Sounds like you are confusing Racks and Chasis.

The Chasis is where the physical cards go but in I/O addressing there is a Rack/Node and the term with Allen bradley products is mostly used with plc 5 equipment.

Physical layouts are chasis. In the slc just connecting expansion chasis with ( a second or more chasis with a cable between them)the slots just continue in a sequential order.

If you have slc chasis that does not have a processsor in the left most slot and has no expansion chasis but does have a comm card in the left most slot then this is a rack of remote I/O being mastered by another plc somewhere.

Check this against your current setup.
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Old November 21st, 2011, 12:31 PM   #4
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Thanks for both of the replies. Sorry, yes when I said rack I did in fact mean chassis. I am aware of the addressing convention with respect to the program. In that the first chassis starts at 0 with the leftmost slot and works up to 29 for the 30th slot in the expansion chassis's.
I don't think My original question was clear. Ignoring program addressing. If say there was an input card in the 1st phyisical slot of the 1st chassis and I connected to say the 1st input on that card. (I know this can't actually happen), then what would the physical address be? From what I have seen and been told it could be any one of a number of answers. Some say that the chassis is 0 some say 1, some say that slot is 0 and again some say 1, also some say the bit number is 0 and others 1. But which is correct? Many thanks.

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Old November 21st, 2011, 12:35 PM   #5
Tim Ganz
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The processor is in slot zero so it would be 1.

On a micrologix or similar it would be zero for the base I/O and 1 for the firt expansion Input card. This is because the I/O and the processor are in the same unit / slot so to speak but in a slc it would always be 1.
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Old November 21st, 2011, 01:11 PM   #6
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BIt numbers on a SLC will always be 0 through 15.

Slot 0 is the CPU or adapter slot for the chassis.

I/O slots are numbered 1-29 for adjacent cards including any extended local chassis (connected to the same backplane with a cable between chassis).

I/O slots hanging off of a remote I/O scanner are a whole nuther animal. After you understand PLC5 rack/group/slot addressing, then those become a combination of the SLC slot number where the scanner card is located, followed by the word delimiter or period, following by the LOGICAL Rack/Group/Slot values used by the PLC-5 system of remote I/O.
It's not all the variables I am most concerned with, it's the undiscovered constants.
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