Bryan L. Programmable controllers. Theory and implementation
Подождите немного. Документ загружается.
349
CHAPTER
9
Programming
Languages
Industrial Text & Video Company 1-800-752-8398
www.industrialtext.com
SECTION
3
PLC
Programming
Table 9-9. Data transfer instructions.
Some PLCs perform a move function to special word table locations. In this
case, the PLC automatically coverts the copied data to the proper numerical
format for the destination location. For example, a register or word might
contain a BCD value that, when transferred to another register or word, is
stored as a binary value, thus executing a BCD-to-binary conversion within
the move instruction.
Another type of move instruction, a move mask (MOVM) instruction, masks
certain bits within the register. Figure 9-100 illustrates this type of move
block. The move mask block transfers the data in register 1000 to register
1100, with the exception of the bits specified by a 0 in the mask register 2000.
Figure 9-99. (a) Move bit and (b) move register functional blocks.
snoitcurtsnIrefsnarTataD
)CLPanihtiwatadlaciremunevomoT:esopruP(
noitcurtsnIlobmySnoitcnuF
evoM
/BVOM/VOM
MVOM/RVOM
enomorfnoitamrofnisrefsnarT
rehtonaotnoitacol
kcolBevoMKBVOM
retsigerfopuorgamorfatadsevoM
noitacolrehtonaotsnoitacol
evoMelbaT
/ELBAT-GER
GER-ELBAT
rokcolbamorfatadsrefsnarT
retsigeraotelbat
—refsnarTkcolB
tuO/nI
REFXKB
deificepsniatadfokcolbaserotS
snoitacolretsigerroyromem
refsnarTIICSAREFXIICSA
aneewtebatadIICSAstimsnarT
CLPadnaecivedlarehpirep
tuOtsriF–nItsriF
refsnarT
OFIF
rofeueuqroelbatastcurtsnoC
atadgnirots
troSTROS
sretsigerfokcolbaniatadehtstroS
redrognidnecsed/gnidnecsani
Reg 1000
Reg 2000
MOVR
10010
MOVB
10010
(b)(a)
Status of bit 15 of register 1000 is
moved to bit 07 of register 2000
Contents of register 1000 are
moved to register 2000 (destination
register can be an I/O register)
Reg 1000
Reg 2000
350
SECTION
3
PLC
Programming
Industrial Text & Video Company 1-800-752-8398
www.industrialtext.com
CHAPTER
9
Programming
Languages
Reg 1000
Mask
Reg 2000
Reg 1100
MOVM
10010
Move with mask
Yet another move instruction found in some controllers is the move status
instruction. This block function transfers system or I/O module status data to
a storage/result register. This information can then be masked, compared, or
examined to determine the status of major or minor faults in the system or an
I/O module. With this information, the controller can take corrective action
through the control program, if necessary.
Figure 9-100.
Move mask functional block.
MOVE BLOCK
A move block (MOVBK) instruction copies a group of register or word
locations from one place to another. The length of the block is generally user-
specified. Figure 9-101 illustrates a move block instruction. When energized,
the control input triggers the execution of this block. The block function then
transfers data from locations 1000 through 1023 (length = 20) to locations
2000 through 2023, respectively. The data in registers 1000 through 1023 is
left unchanged. In some PLCs, the user can specify how many locations can
be transferred during one scan (rate per scan).
Figure 9-101. Move block functional block.
Reg: 1000 = 0110 1000 1001 0101
Reg: 2000 = 0000 0000 1111 0000 Mask
Reg: 1100 = 0000 0000 1001 0000
onl
y
bits passed
Reg 1000
Length 20
Reg 2000
MOVBK
10010
Reg 1000
Reg 1001
Reg 1023
Reg 2000
Reg 2001
Reg 2023
Move
351
CHAPTER
9
Programming
Languages
Industrial Text & Video Company 1-800-752-8398
www.industrialtext.com
SECTION
3
PLC
Programming
TABLE MOVE
A table move instruction transfers data from a block or table to a register or
word in memory. There are two types of table move instructions: table-to-
register (TABLE-REG) and register-to-table (REG-TABLE). The main
characteristic of a table move block is the manipulation of a pointer register,
which specifies the particular table location in which the register or word
value will be stored. Figure 9-102 shows a table move block.
Figure 9-102. (a) Table-to-register and (b) register-to-table functional block.
TABLE REG
10010
Reg 2000
Length 08
Pointer 1000
Reg 3000
Control
10111
Increment
Pointer
12
Reset
Pointer
Enable
End of
table
10010
Reg 3000
Pointer 1000
Reg 2000
Length 08
Control
10111
Increment
Pointer
12
Reset
Pointer
Enable
End of
table
TABLEREG
9876
3760
Reg 2000
Reg 2003
Reg 2007
Table
9876
4
Reg 3000
Reg 1000
Destination
Register
Pointer
Register
Pointer register points to
4th location (Reg 2003)
and transfers its contents
to register 3000.
5876
Reg 2000
Reg 2002
Reg 2007
Table
3 Reg 1000
Pointer
Register
Pointer register points to
3rd location (Reg 2002)
and transfers its contents
to register 3000.
9876
3760
Reg 2000
Reg 2004
Reg 2007
Table
5 Reg 1000
Pointer
Register
Pointer register points to
5th location (Reg 2004)
and transfers its contents
to register 3000.
5876
9850
Reg 2000
Reg 2003
Reg 2007
Table
4 Reg 1000
Pointer
Register
Pointer register points to
4th location (Reg 2003)
and transfers its contents
to register 3000.
5876 Reg 3000
Source
Register
3760 Reg 3000
Destination
Register
9850 Reg 3000
Source
Register
(a) (b)
9876
352
SECTION
3
PLC
Programming
Industrial Text & Video Company 1-800-752-8398
www.industrialtext.com
CHAPTER
9
Programming
Languages
EXAMPLE 9-11
A batching system operates during an eight-hour shift, where several
batch sizes are processed at the rate of approximately one batch per
hour. Implement instructions to store the batch information, including
the batch size in gallons and the time of day when the batch was
finished. Register 1000 holds the value of the total batch, while register
1500 holds the time of day (in hours and minutes) in BCD format
(HHMM).
S
OLUTION
Figure 9-103 illustrates a register-to-table instruction that will transfer
the outputs of registers 1000 and 1500, using the same pointer register
to store the information to two tables simultaneously. This ensures that
the pointer points to a batch amount that corresponds to the time of the
batch (see Figure 9-104). The Batch Done signal, perhaps coming
from the opening of the discharge valve, triggers the register-to-table
instruction. Once the storing of the register into the table has taken
place, the instruction’s enable/done output increments the pointer.
The pointer is incremented in only one of the blocks to avoid a double
The transition of the control input from OFF to ON enables a table move
instruction, which then increments the contents of the pointer register every
time the middle input, the increment (INCR) pointer, transitions from OFF to
ON. The bottom input of the table move block resets the pointer to zero
(initialize to top of table). If data must be stored to or retrieved from a specific
table location, the pointer register can be loaded with the appropriate value,
which points to the specified location. A set parameter or move register
instruction loads this information prior to the table move.
Referencing Figure 9-102, the length specifies the number of word locations
in the table to be moved (8 in this example), beginning at the starting location
(register 2000). After the table move block transfers the data from these eight
locations, it energizes the top output. It energizes the middle output when the
pointer register has reached the end of the table.
Applications of the table move instruction include the loading of new data
into a table, the storage of input information (e.g., analog) from special
modules, and the input of error information from a controlled process. It is
also useful when changing preset parameters in timers and counters and
when simultaneously driving a group of 16 outputs through I/O registers. A
table move instruction is also used when looking up values in a table for
comparison, linear interpolation, etc.
353
CHAPTER
9
Programming
Languages
Industrial Text & Video Company 1-800-752-8398
www.industrialtext.com
SECTION
3
PLC
Programming
Figure 9-103. Register-to-table instruction used for storing batch information.
increment. The increment occurs after both register-to-table instruc-
tions have been executed to ensure that the data is stored by the same
pointer counter. Note that the Batch Done signal is a transitional
contact, so the register-to-table instruction only transfers the register
data once to its appropriate table location.
Figure 9-104. Table 3000 stores batch sizes and table 4000 stores the time of day
the batches were completed.
323
401
378
303
350
400
320
318
R3000
R3001
R3002
R3003
R3004
R3005
R3006
R3007
1
2
3
4
5
6
7
8
Table 3000
Table
8-Hour Shift
Batch
(in gallons)
0714
0823
0914
1017
1130
1224
1330
1422
R4000
R4001
R4002
R4003
R4004
R4005
R4006
R4007
1
2
3
4
5
6
7
8
Table 4000
Table
Time of Day
Time
(in hr: min)
Reg 1000
Pointer 2000
Reg 3000
Length 08
400Batch Done
TABLEREG
Control
401
Incr
New Day
Reset
Reg 1500
Pointer 2000
Reg 4000
Length 08
402Batch Done
TABLEREG
Control
403402
Incr
New Day
Reset
354
SECTION
3
PLC
Programming
Industrial Text & Video Company 1-800-752-8398
www.industrialtext.com
CHAPTER
9
Programming
Languages
Figure 9-106. Block transfer in instruction.
BLOCK TRANSFER—IN/OUT
Some PLCs provide block transfer (BXFER) instructions, which are prima-
rily used with special I/O modules to transfer blocks of data. The two basic
types of block transfers are block transfer in and block transfer out. Figure
9-105 shows a block transfer in/out instruction. The module address location
of the transfer data may be explicitly marked as the rack and slot location of
the interface. For example, the block transfer input in Figure 9-106 shows that
the contents to be read from the intelligent module (rack 01, slot 03, 8
channels) will be stored in registers 1000 through 1007.
Figure 9-105. Block transfer in/out functional block.
Rack
Slot
Length
Register
Enable/Done
BKXFER
IN or OUT
The rack and slot indicate the location of
the input or output module. The rack and
slot entries in the block may be combined
into one address in some PLCs.
BKXFER IN
10010
Rack 01
Slot 03
Length 08
Reg 1000
Channel 0
Channel 1
Channel 2
Channel 3
Channel 4
Channel 5
Channel 6
Channel 7
1000
1001
1002
1003
1004
1005
1006
1007
Contents Register
Processor and
Power Supply
00 01 02 03 04 05 06 07 Slot
Rack 01
355
CHAPTER
9
Programming
Languages
Industrial Text & Video Company 1-800-752-8398
www.industrialtext.com
SECTION
3
PLC
Programming
The control input activates an ASCII transfer (in or out) instruction. When
reading data, the instruction allows the special I/O module to perform a read
function. The processor then reads the data from the module and stores it in
special memory locations (from the first register to the last, as specified by
the length). The I/O address in the block indicates the location of the
module. When writing data, the processor transfers information from the
location where it is stored to the address where the module is located.
Figure 9-107. ASCII transfer in/out functional block.
ASCII TRANSFERS
An ASCII transfer (ASCII XFER) instruction transmits ASCII-formatted
data between a PLC and a peripheral device. This functional block, which is
under program control, operates in conjunction with an ASCII communica-
tions module. The communication of ASCII data usually occurs in two ways:
reading data from a peripheral or writing data to a peripheral. This functional
block is widely used in applications that require report generation. Figure
9-107 illustrates a typical read/write ASCII functional block.
The control input, when enabled, executes a block transfer instruction. During
a block transfer in function, the instruction stores data about the I/O module
in memory locations or registers starting at the specified register location. The
block length specifies how many locations are needed to store the I/O module
data. For example, the data from an analog input module with four input
channels can be read all at once, if the length is specified as four. A block
transfer out instruction operates in a similar manner, with the address of the
output module determining the destination of the data transfer. The top output
of the block transfer instruction, when energized, signals the completion of
the transfer operation.
ASCII
XFER (IN/OUT)
10010
Reg 4000
Length 64
Rack 01
Slot 04
A total of 64 ASCII characters are sent (XFER OUT)
or received (XFER IN). Each register location holds 2
characters (one character per byte).
356
SECTION
3
PLC
Programming
Industrial Text & Video Company 1-800-752-8398
www.industrialtext.com
CHAPTER
9
Programming
Languages
Figure 9-108. FIFO functional block.
Some ASCII transfer instructions use a pointer register to access specific
characters in the table (e.g., to decode a specific input character from the data
table). Other ASCII instructions allow the user to specify how many bytes or
characters are transmitted during a scan. The speed of transmission (baud
rate) is a function of the scan time, which depends on the number of ASCII
devices that are active at one time. An ASCII transfer instruction assumes that
proper baud rates, start/stop bits, and parity have been established in the I/O
module hardware.
FIFO STACK TRANSFERS
A first-in–first-out (FIFO) instruction constructs a table or queue where data
is stored. The basic function of this operation is similar to a shift register
instruction, in which one word (16 bits) is shifted within the stack each time
the instruction is executed. The data is always shifted in the order in which it
was received—the first word shifted in will be the first word shifted out. FIFO
is, in essence, a first-come–first-served format. Figure 9-108 shows a typical
FIFO block instruction.
9000
9001
9002
9003
9004
9005
9006
9007
Reg 1000
1001
1002
1003
1004
1005
1006
Reg 1007
Reg 2000
7777
Contents
Reg 3000
Before FIFO Shift
7777
9000
9001
9002
9003
9004
9005
9006
Reg 1000
1001
1002
1003
1004
1005
1006
Reg 1007
Reg 2000
Contents
Reg 3000
After FIFO Shift
9007
FIFO (IN/OUT)
10010
Reg IN 2000
Length 08
Reg Stack 2000
Reg OUT 3000
Control
Enable
10120
Reset
End of
table
357
CHAPTER
9
Programming
Languages
Industrial Text & Video Company 1-800-752-8398
www.industrialtext.com
SECTION
3
PLC
Programming
A FIFO operation consists of two parts: a FIFO input (FIFO IN) instruction
and a FIFO output (FIFO OUT) instruction. The FIFO IN instruction loads
the queue, while the FIFO OUT instruction unloads it. FIFO instructions are
useful for storing, and later retrieving, large groups of temporary data as it is
received. A typical application of a FIFO instruction is the storage and
retrieval of data that is synchronized to the external movement of parts on a
conveyor or transfer machine.
An OFF-to-ON transition of the control input logic initiates a FIFO block.
Some blocks may have a reset signal to reset the FIFO stack (clear stack). For
a FIFO instruction, the register in holds the data that will be transferred to
the queue. This data is placed in the FIFO stack when the control input is ON.
The data in the last position of the stack is output through the register out. The
FIFO length specifies the length of the stack.
The FIFO instruction is very useful when trying to keep the values obtained
from a process in a “moving window.” For example, Figure 9-109 illustrates
a temperature profile as a function of time. If the desired window is from t
0
to t
1
, the values can be kept in a FIFO stack. Thus, the stack will always contain
the last t
0
–t
1
values.
Figure 9-109. Temperature profile.
SORT
The sort (SORT) block function sorts a block of registers, in ascending or
descending order, according to their contents. Figure 9-110 shows a sort block
in which the closing of contact 10 enables the instruction. This block sorts
registers 1000 through 1017 in ascending order and then stores the results in
registers 2000 through 2017. This type of function is very useful when
Temperature Out
Temperature
Temperature In
Temperature at time
t
0
Temperature
values stored
Temperature at time
t
1
°C
High Limit
Low Limit
Time Window
t
0
t
1
Time
358
SECTION
3
PLC
Programming
Industrial Text & Video Company 1-800-752-8398
www.industrialtext.com
CHAPTER
9
Programming
Languages
SEQUENCERS
computing the median of sample readings—an operation that requires the
sample to be in numerical order. PLCs provide either ascending, descending,
or both types of sorting.
Figure 9-110. Ascending sort functional block.
9-13 SPECIAL FUNCTION INSTRUCTIONS
As the name implies, special function instructions perform operations that
do not fall under any other PLC instruction categories. These functions are
usually available in medium to large controllers. Table 9-10 lists the common
special function instructions.
Table 9-10. Special function instructions.
A sequencer (SEQ) block is a powerful instruction that simulates a drum
timer. A sequencer is analogous to a music box mechanism, in which each peg
produces a tone as the cylinder rotates and strikes the resonators. In a sequencer,
each peg (bit) can be interpreted as a logic 1 and no peg as a logic 0.
A sequencer table, which is similar to a spread-out music box cylinder,
provides sequencer information. Figure 9-111 illustrates a cylinder and
sequencer table comparison. The number of bits in a sequencer can vary from
snoitcurtsnInoitcnuFlaicepS
)CLPanisnoitarepodezilaicepswollaoT:esopruP(
noitcurtsnIlobmySnoitcnuF
recneuqeSQES
nevird-emitaniatadstuptuO
rennamnevird-tnevero
citsongaiDGAID
atadtupnilautcaserapmoC
atadecnereferhtiw
-largetnI-lanoitroporP
evitavireD
DIP
lortnocpool-desolcsedivorP
ssecorpafo
SORT (ASC)
100010
Source Reg 1000
Length 16
Reset Reg 2000