Page 281 - Programmable Logic Controllers, Fifth Edition - Mobile version

• Data are copied from file #B3:0 at the bit
locations through mask word, F0FF hex or
1111000011111111 binary, to the destination
O:2. Mask bits are set to 1 to pass data and reset
to 0 to mask data.
• Once the position reaches the last position on the
true-to-false transition of the instruction the position
will reset to 1.
Figure 12-16 Sequencer file #N7:10 timer settings. • Note that the data in O:2 match the data in
Source: Courtesy of TheLearningPit
position 2 in the file, except for the data in bits
8 through 11.
With an event-driven sequencer, the SQO instruction
advances to the next step by an external pulsed input event • Bits 8 through 11 may be controlled from else-
rather than a preset time. An example of an event-driven where in the program; they are not affected by the
sequencer is shown in Figure 12-18. The operation of the sequencer instruction because of the 0 in these bit
program can be summarized as follows: positions in the mask.
The sequencer compare (SQC) instruction is an out-
• The sequencer SQO instruction uses two OR con- put instruction used to compare bits from an input source
figured sensor switches (S1 and S2). file to corresponding bits from data words in a sequencer
• Any one of the two parallel paths can make the file. When the pairs of bits are the same, then the found
SQO rung true. (FD) bit in the control register is set to 1. This instruction
• As each event occurs, that OR branch makes a can be used to compare the status of a machine’s input
false-to-true transition advancing the sequencer devices with what is required for normal operation. When
position. the status of the input devices on the machine (on or off)

Input Ladder logic program
O:2 L2
SW T4:0/DN TON
L1 TIMER ON DELAY EN 0
Timer T4:1 1
SW Time base 1.0 DN 2
Preset 3 3
Accumulated 0 4
5
SQO 6
T4:0/DN
SEQUENCER OUTPUT 7
File #B3:0 EN 8
Mask 0FFFFh 9
Dest O:2.0 DN 10
Control R6:0 11
Length 8
Position 0 12
13
14
15

Figure 12-17 Time-driven sequencer with constant time interval between steps.
Source: Courtesy of TheLearningPit

262 Chapter 12 Sequencer and Shift Register Instructions

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