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14
are assigned the word shaded below them which they write and can be writ-
ten by the other PCs.
PC Link Unit 1
PC Link Unit 3
C2000H CPU Rack
C500 CPU Rack C500 CPU Rack
C200H CPU Rack
PC Link Unit 2
PC Link Unit 0
LR 08 to LR 15
C2000H CPU
Unit 0
C500 CPU
Unit 1
C500 CPU
Unit 2
C200H CPU
Unit 3
LR 00 to LR 07
LR 16 to LR 23
LR 24 to LR 31
LR 32 to LR 63 LR 32 to LR 63
LR 08 to LR 15
LR 00 to LR 07
LR 16 to LR 23
LR 24 to LR 31
LR 08 to LR 15
LR 00 to LR 07
LR 16 to LR 23
LR 24 to LR 31
LR 08 to LR 15
LR 00 to LR 07
LR 16 to LR 23
LR 24 to LR 31
LR 08 to LR 15
LR 00 to LR 07
LR 16 to LR 23
LR 24 to LR 31
Useable
as work
bits
Useable
as work
bits
The C200H could be replaced by the C200HS and C200HX/HG/HE(-Z) with-
out any changes in this example.
In a Multilevel PC Link System, only half of the LR area in each PC is used
for communications in any one PC Link Subsystem. The first half of the
words (from word 00) is used by the Subsystem assigned operating level 0;
the second half, by the Subsystem assigned operating level 1. This is true
regardless of whether or not a PC is actually in two Subsystems. In the ex-
ample on the next page, the two C500s do not use LR words 16 through 31
because they are not in a Subsystem in operating level 1. If another PC Link
Unit was later added to either PC, these words would be available for use by
it. The number of words used by a Subsystem is thus half of the number of
words provided by the PC with the smallest LR area.
Once the words used in a Subsystem are determined, the process is the same
as for any other PC Link System: words common to all of the PCs in a Subsystem
are divided evenly among the PC Link Units, with unit numbers determining
which words are allocated to which Unit. Again, the Unit assigned number 0 in
each Subsystem is the polling unit for that Subsystem.
Below are provided the system configuration, unit numbers, operating levels,
and word allocations for each PC Link Unit in a Multilevel System. The vertical
bars represent the LR area in each PC. Arrows indicate data flow from the words
written to by each PC. Write words for each PC have been shaded.
In the Subsystem assigned operating level 1, LR words 56 through 63 are not
used for PC Link communications because switch settings are available only for
2, 4, 8, or 16 PC Link Units per Subsystem. If a fourth PC was added to this Sub-
system, it would be assigned these words.
Although not used by the PC Link System, words labeled “not used” may be
used as work words in programming to manipulate data within the CPU.
Note
LR Area Allocations in
Multilevel Systems
LR Area Allocations Section 3-2