29
Bit number
Word 000
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
Word 001
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
15
14
13
12
11
10
09
08
07
06
05
04
03
02
01
00
To designate data by word, all that is necessary is the acronym (if required)
and the two-digit word address. To designate data by bit, the word address is
combined with the bit number as a single four-digit address. The following
table show examples of this. The two rightmost digits of a bit designation
must indicate a bit between 00 and 15, i.e., the rightmost digit must be 5 or
less the next digit to the left, either 0 or 1.
The same TC number can be used to designate either the present value (PV)
of the timer or counter, or a bit that functions as the Completion flag for the
timer or counter.
Area
Word designation
Bit designation
I/O, work, and
dedicated bits
00
0015 (leftmost bit in word 00)
TC
TC 03 (designates PV)
TC 03 (designates Completion Flag)
LR
LR 07
LR 0000
DR
DR 15
DR 0513
Word data input as decimal values is stored in binary-coded decimal (BCD);
word data entered as hexadecimal is stored in binary form. Each four bits of
a word represents one digit, either a hexadecimal or decimal digit, numerical-
ly equivalent to the value of the binary bits. One word of data thus contains
four digits, which are numbered from right to left. These digit numbers and
the corresponding bit numbers for one word are shown below.
Bit number
Contents
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
15
14
13
12
11
10
09
08
07
06
05
04
03
02
01
00
Digit number
3
2
1
0
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
binary 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. 3-7 Instruction Set specifies when a particular
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.
Binary 1111 is hexadecimal F; binary 0101 is hexadecimal 5. The hexadeci-
mal 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 are easily converted back and forth. In this case, each
BCD digit (i.e., each group of four BCD bits) is numerically equivalent of the
corresponding decimal digit. The BCD bits 0101011101010111 are converted
Data Structure
Converting Different Forms
of Data
Memory Areas
Section 3-2