40
Group-2 B7A Interface Units are allocated words between IR 030 and IR 049
according to I/O number settings made on them and do not use the words allo-
cated to the slots in which they are mounted. For 32-point Units, each Unit is allo-
cated two words; for 64-point Units, each Unit is allocated four words. The words
allocated for each I/O number are in the following tables. Any words or part of
words not used for I/O can be used as work words or bits in programming.
32-point Units 64-point Units
I/O number
Words I/O number Words
0 IR 30 to IR 31 0 IR 30 to IR 33
1 IR 32 to IR 33 1 IR 32 to IR 35
2 IR 34 to IR 35 2 IR 34 to IR 37
3 IR 36 to IR 37 3 IR 36 to IR 39
4 IR 38 to IR 39 4 IR 38 to IR 41
5 IR 40 to IR 41 5 IR 40 to IR 43
6 IR 42 to IR 43 6 IR 42 to IR 45
7 IR 44 to IR 45 7 IR 44 to IR 47
8 IR 46 to IR 47 8 IR 46 to IR 49
9 IR 48 to IR 49 9 Cannot be used.
When setting I/O numbers on the B7A Interface Units, be sure that the settings
will not cause the same words to be allocated to more than one Unit. For exam-
ple, if I/O number 0 is allocated to a 64-point Unit, I/O number 1 cannot be used
for any Unit in the system.
Group-2 B7A Interface Units are not considered Special I/O Units and do not af-
fect the limit to the number of Special I/O Units allowed in the System, regardless
of the number used.
4-2 Remote I/O
There are limits to how long the normal wiring between the PC and its Expansion
I/O Racks can be. A Remote I/O Unit can extend this distance greatly, so that the
PC and its Expansion I/O Racks can even be located in separate buildings.
There are two types of Remote I/O Systems, optical and wired.
By locating a Rack farther from the CPU Rack, a Remote I/O System eliminates
the time and mess in wiring (or changing wiring) to many devices that are sepa-
rated from the CPU Rack. Although all I/O points must ultimately be wired indi-
vidually, the question is one of distance: Do you want to wire dozens of terminals
all the way across a factory complex or do you want to run a single cable for most
of the distance and then wire individual terminals locally? A PC with an Expan-
sion I/O System is called an Expanded PC.
Allocation for Group-2 B7A
Interface Units
Remote I/O Section 4-2
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