Omron CPM1 - PROGRAMING MANUAL 02-2001 Programming Manual page 354

Basic Ladder Diagrams
Execution Conditions
Operand Bits
Logic Blocks
Instruction Block
6-3-2 Mnemonic Code
Program Memory Structure
336
bit is ON, and a normally closed condition when you want something to happen
when a bit is OFF.
00000
Normally open
condition
00000
Normally closed
condition
In ladder diagram programming, the logical combination of ON and OFF condi-
tions before an instruction determines the compound condition under which the
instruction is executed. This condition, which is either ON or OFF, is called the
execution condition for the instruction. All instructions other than LOAD instruc-
tions have execution conditions.
The operands designated for any of the ladder instructions can be any bit in the
IR, SR, HR, AR, LR, or TC areas. This means that the conditions in a ladder dia-
gram can be determined by I/O bits, flags, work bits, timers/counters, etc. LOAD
and OUTPUT instructions can also use TR area bits, but they do so only in spe-
cial applications. Refer to 6-3-8 Branching Instruction Lines for details.
The way that conditions correspond to what instructions is determined by the
relationship between the conditions within the instruction lines that connect
them. Any group of conditions that go together to create a logic result is called a
logic block. Although ladder diagrams can be written without actually analyzing
individual logic blocks, understanding logic blocks is necessary for efficient pro-
gramming and is essential when programs are to be input in mnemonic code.
An instruction block consists of all the instructions that are interconnected
across the ladder diagram. One instruction block thus consists of all the instruc-
tions between where you can draw a horizontal line across the ladder diagram
without intersecting any vertical lines and the next place where you can draw the
same type of horizontal line.
The ladder diagram cannot be directly input into the PC via a Programming Con-
sole; the SSS is required. To input from a Programming Console, it is necessary
to convert the ladder diagram to mnemonic code. The mnemonic code provides
exactly the same information as the ladder diagram, but in a form that can be
typed directly into the PC. Actually you can program directly in mnemonic code,
although it in not recommended for beginners or for complex programs. Also,
regardless of the Programming Device used, the program is stored in memory in
mnemonic form, making it important to understand mnemonic code.
Because of the importance of the Programming Console as a Programming De-
vice and because of the importance of mnemonic code in complete understand-
ing of a program, we will introduce and describe the mnemonic code along with
the ladder diagram. Remember, you will not need to use the mnemonic code if
you are inputting via the SSS (although you can use it with the SSS if you prefer).
The program is input into addresses in Program Memory. Addresses in Program
Memory are slightly different to those in other memory areas because each ad-
dress does not necessarily hold the same amount of data. Rather, each address
holds one instruction and all of the definers and operands (described in more
Instruction is executed
Instruction
when IR bit 00000 is ON.
Instruction is executed
Instruction
when IR bit 00000 is OFF.
Section 6-3