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When referring to the entire word, the digit numbered 0 is called the right-
most digit; the one numbered 3, the leftmost digit.
When inputting data into data areas, it must be input in the proper form for
the intended purpose. This is no problem when designating individual bits,
which are merely turned ON (equivalent to a binary value of 1) or OFF (a bi-
nary value of 0). When inputting word data, however, it is important to input it
either as decimal or as hexadecimal, depending on what is called for by the
instruction it is to be used for.
Section 5 Instruction Set
specifies when a par-
ticular form of data is required for an instruction.
Binary and hexadecimal can be easily converted back and forth because
each four bits of a binary number is numerically equivalent to one digit of a
hexadecimal number. The binary number 0101111101011111 is converted to
hexadecimal by considering each set of four bits in order from the right. Bi-
nary 1111 is hexadecimal F; binary 0101 is hexadecimal 5. The hexadecimal
equivalent would thus be 5F5F, or 24,415 in decimal (16
3
x 5 + 16
2
x 15 + 16
x 5 + 15).
Decimal and BCD can also be easily converted back and forth. In this case,
each BCD digit (i.e., each four BCD bits) is numerically equivalent of the cor-
responding decimal digit. The BCD bits 0101011101010111 are converted to
decimal by considering each four bits from the right. Binary 0101 is decimal
5; binary 0111 is decimal 7. The decimal equivalent would thus be 5,757.
Note that this is not the same numeric value as the hexadecimal equivalent
of 0101011101010111, which would be 5,757 hexadecimal, or 22,359 in deci-
mal (16
3
x 5 + 16
2
x 7 + 16 x 5 + 7).
Because the numeric equivalent of each four BCD binary bits must be
equivalent to a decimal value, any four bit combination numerically greater
then 9 cannot be used, e.g., 1011 is not allowed because it is numerically
equivalent to 11, which cannot be expressed as a single digit in decimal nota-
tion. The binary bits 1011 are of course allowed in hexadecimal and they are
equivalent to the hexadecimal digit C.
There are instructions provided to convert data in either direction between
BCD and hexadecimal. Refer to
5-15 Data Conversion
for details. Tables of
binary equivalents to hexadecimal and BCD digits are provided in the appen-
dices for reference.
Decimal points are used in timers only. The least significant digit represents
tenths of a second. All arithmetic instructions operate on integers only.
3-3 Internal Relay (IR) Area
The IR area is used both to control I/O points and as work bits to manipulate
and store data internally. It is accessible both by bit and by word. Those
words that can be used to control I/O points are called I/O words. Bits in I/O
words are called I/O bits.
The number of I/O words varies between the K-type PCs. As shown, the IR
area is comprised of three main sections. These are input words, output
words and work words (work bits). Work bits are used in programming to ma-
nipulate data and control other bits. IR area work bits are reset when power
is interrupted or PC operation is stopped.
Converting Different Forms
of Data
Decimal Points
Internal Relay (IR) Area Section 3-3