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3-3-1 I/O Area
The I/O Area is used as data to control I/O points. Those words that are used to
control I/O points are called I/O words. Bits in I/O words are called I/O bits. I/O
Area bits that are not allocated as I/O bits are reset when power is interrupted or
PC operation is stopped. I/O Area word addresses run from CIO 0000 through
CIO 0127 (I/O bits CIO 000000 through CIO 012715).
The maximum number of I/O bits is 16 (bits/word) times the number of I/O words,
i.e., 2,048 bits. I/O bits are assigned to input or output points on Units connected
at various locations in the PC System, as described later in this section (see
Word Allocations).
If an I/O point on a Unit brings an input into the PC, the bit assigned to it is an input
bit; if the point sends an output from the PC, the bit assigned to it is an output bit.
To turn ON an output, the output bit assigned to it must be turned ON from the
program or from a Programming Device. When an input turns ON, the input bit
assigned to it also turns ON and the status of the input can be accessed indirect-
ly by reading the status of the input bit assigned to it. Input status and control
output status is thus manipulated through I/O bits.
After the I/O Table has been registered (see Word Allocations, below), an “I” will
appear before input bit addresses and a “Q” will appear before output bit ad-
dresses on SSS (SYSMAC Support Software) displays.
I/O bits that are not assigned to I/O points can be used as work bits.
Input bits record external signals input to the PC and can be used in any order in
programming. Each input bit can also be used in as many instructions as re-
quired to achieve effective and proper control. They cannot be used as oper-
ands in instructions that control bit status, e.g., the OUTPUT, DIFFERENTIATE
UP, and KEEP instructions. In other words, input bits should be treated as read-
only bits.
Output bits are used to output program execution results and can be used in any
order in programming. Generally speaking, any one output bit should be used in
only one instruction that controls its status, including OUT, KEEP(11), DIFU(13),
DIFD(14), and SFT(10). If an output bit is used in more than one such instruction,
only the status determined by the last instruction will actually be output from the
PC during the normal I/O refresh period.
If you control the status of an output bit in more than one instruction, be sure to
consider proper output timing and test the program before actual application.
See 5-14-1 SHIFT REGISTER – SFT(050) for an example that uses an output
bit in two “bit-control” instructions.
I/O words in the CIO Area are allocated to Units mounted on Racks or otherwise
connected to the PC by performing the I/O Table Registration operation. This
operation creates in memory a table called an I/O table that records what words
and how many words are allocated to the Units and whether these words are
input or output words. The actual procedure for this operation is described in the
SSS Operation Manuals.
The first word allocated to each Rack can be set with the SSS under the PC Set-
up. When the I/O Table Registration operation is performed, the system assigns
word addresses to Units in the order in which they are mounted left to right on
each Rack, beginning with the first word set in the PC Setup. The assigned
words must be between CIO 0000 and CIO 0511.
For any Racks not assigned a first word in the PC Setup menu when the I/O
Table is registered, the system automatically assigns word addresses to Units.
I/O Words
Input Bit Usage
Output Bit Usage
Word Allocations
CIO (Core I/O) Area
Section 3-3
Summary of Contents for CVM1D
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