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used to store execution conditions at branching points in ladder diagrams.
The use of TR bits is described in
Section 4 Writing and Inputting the Pro-
gram.
The TC area consists of TC numbers, each of which is used for a spe-
cific timer or counter defined in the program. Refer to
3-7 Timer/Counter (TC)
Area
for more details on TC numbers and to
5-11 Timer and Counter Instruc-
tions
for information on actual application.
The rest of the data areas (i.e., the IR, SR, HR and DM areas) consist of
words, each of which consists of 16 bits numbered 00 through 15 from right
to left. IR words 00 and 01 are shown below with bit numbers. Here, the con-
tent of each word is shown as all zeros. Bit 00 is called the rightmost bit; bit
15, the leftmost bit.
Bit number 15 14 13 12 11 10 09 08 07 06 05 04 03 02 01 00
IR word 00 0000000000000000
IR word 01 0000000000000000
The term least significant is often used for rightmost; the term most signifi-
cant, for leftmost. These terms have not been used in this manual because a
single word is often split into two or more parts, with each part used for differ-
ent parameters or operands, sometimes even with bits in another word.
When this is done, the rightmost bits in a word may actually be the most sig-
nificant bits, i.e., the leftmost bits, of a value with other bits, i.e., the least sig-
nificant bits, contained in another word.
The DM area is accessible by word only; you cannot designate an individual
bit within a DM word. Data in the IR, SR and HR areas is accessible either by
bit or by word, depending on the instruction in which the data is being used.
To designate one of these areas by word, all that is necessary is the acronym
(if required) and the one or two-digit word address. To designate an area by
bit, the word address is combined with the bit number as a single three- or
four-digit address. The examples in the following table should make this
clear. The two rightmost digits of a bit designation must indicate a bit be-
tween 00 and 15.
The same TC number can be used to designate either a word containing the
present value (PV) of the timer or counter or a bit that functions as the com-
pletion flag for the timer or counter. This is explained in more detail in
3-7
Timer/Counter (TC) Area
.
Area Word designation Bit designation
IR 00 0015 (leftmost bit in word 00)
SR 19 1900 (rightmost bit in word 19)
DM DM 10 Not possible
TC TC 46 (designates PV) TC 46 (designates completion flag)
Word data input as decimal values is stored in binary-coded decimal (BCD)
code; word data input as hexadecimal is stored in binary form. Because each
word contains 16 bits, each four bits of a word represents one digit: either a
hexadecimal digit equivalent numerically to the binary bits or decimal. 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 0000000000000000
15 14 13 12 11 10 09 08 07 06 05 04 03 02 01 00
Digit number 3210
Note
Data Structure
Data Area Structure Section 3-2