Lec 9 - Shift and Sequencer Instructions PDF

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Programmable Logic Controllers Shift and Sequencer Instructions

Electrical & Computer Engineering

Dr. D. J. Jackson Lecture 9-1

Application Specific Instructions • Bit Shift Instructions – Allows for basic shift and rotate operations – Bit Shift Left (BSL) – Bit Shift Right (BSR)

• Sequencer Instructions – Useful for outputting or comparing a sequence of data on a recurring basis – Sequencer Output (SQO) – Sequencer Compare (SQC) – Sequencer Load (SQL)

Electrical & Computer Engineering

Dr. D. J. Jackson Lecture 9-2

9-1

Bit Shift Instructions Overview • Entering Parameters • File is the address of the bit array you want to manipulate. You must use the file indicator (#) in the bit array address. • Control is the control element that stores the status byte of the instruction and the size of the array (in number of bits). • Note that the control address should not be used for any other instruction. • The control element is shown below.

Electrical & Computer Engineering

Dr. D. J. Jackson Lecture 9-3

Status Bits • Status bits of the control element may be addressed by mnemonic (UL, ER, DN, EN). They include: • Unload Bit UL (bit 10) stores the status of the bit exited from the array each time the instruction is enabled. • Error Bit ER (bit 11), when set, indicates the instruction detected an error such as entering a negative number for the length or position. Avoid using the output bit when this bit is set. • Done Bit DN (bit 13), when set, indicates the bit array has shifted one position. • Enable Bit EN (bit 15) is set on a false-to-true transition of the rung and indicates the instruction is enabled. • When the register shifts and input conditions go false, the enable, done, and error bits are reset.

Electrical & Computer Engineering

Dr. D. J. Jackson Lecture 9-4

9-2

Bit Address and Array Length • Bit Address is the address of the source bit that the instruction inserts in the first (lowest) bit position (BSL) or the last (highest) bit position (BSR). • Length (size of bit array) is the number of bits in the bit array, up to 2048 bits. • A length value of 0 causes the input bit to be transferred to the UL bit. – For SLC processors, the length is 2048. – For MicroLogix 1000 series controllers, this length is 1680.

• A length value that points past the end of the programmed file causes a runtime major error to occur. Electrical & Computer Engineering

Dr. D. J. Jackson Lecture 9-5

Bit Shift Left (BSL) and Bit Shift Right (BSR) • BSL and BSR are output instructions that load data into a bit array one bit at a time. • The data is shifted through the array, then unloaded one bit at a time.

Electrical & Computer Engineering

Dr. D. J. Jackson Lecture 9-6

9-3

Bit Shift Left Instruction

Electrical & Computer Engineering

Dr. D. J. Jackson Lecture 9-7

Using BSL • When the rung goes from false-to-true, the processor sets the enable bit (EN bit 15) and the data block is shifted to the left (to a higher bit number) one bit position. • The specified bit at the bit address is shifted into the first bit position. • The last bit is shifted out of the array and stored in the unload bit (UL bit 10). • For wraparound operation, set the position of the bit address to the last bit of the array or to the UL bit. Electrical & Computer Engineering

Dr. D. J. Jackson Lecture 9-8

9-4

BSR Example

Electrical & Computer Engineering

Dr. D. J. Jackson Lecture 9-9

Sequencer Instructions • These instructions transfer 16-bit data to word addresses for the control of sequential machine operations • Essentially these instructions provide a capability for implementing multi-bit state machines • An example use is in the traffic control light problem

Electrical & Computer Engineering

Dr. D. J. Jackson Lecture 9-10

9-5

Sequencer Output and Compare • When the rung transfers from false-to-true the instruction is incremented to the next step in the sequencer file. • Data from the sequencer file is then transferred through a mask and into the destination address specified in the command. • The data is updated during each scan that the rung remains true. • When the last word in the sequencer file is transferred the done bit is set. • On the next transition from false-to-true for the rung the instruction is reset to step one

Electrical & Computer Engineering

Dr. D. J. Jackson Lecture 9-11

Sequencer Parameters • Entering Parameters • File is the address of the sequencer file. You must use the file indicator (#) for this address. • Mask (SQO, SQC) is a hexadecimal code or the address of the mask word or file through which the instruction moves data. – Set mask bits to pass data and reset mask bits to mask data. – If the mask is a file, its length will be equal to the length of the sequencer file. – The two files track automatically.

• Source is the address of the input word or file for a SQC from which the instruction obtains data for comparison to its sequencer file. • Destination is the address of the output word or file for a SQO to which the instruction moves data from its sequencer file.

Electrical & Computer Engineering

Dr. D. J. Jackson Lecture 9-12

9-6

Sequencer Control • Control (SQO, SQC) is the control structure that stores the – status byte of the instruction, – the length of the sequencer file, – and the instantaneous position in the file.

• You should not use the control address for any other instruction.

Electrical & Computer Engineering

Dr. D. J. Jackson Lecture 9-13

Sequencer Status Bits • CONTROL – The control parameter is a structure to store the: status byte of the instruction, length of the sequencer file, and the instantaneous position in the file. The control address can not be used for any other instruction. – Error Bit ER (11) • This bit is set when the processor detects a negative position value, or a negative or zero length value. This results in a major error if not cleared before the END or TND instruction is executed.

– Done Bit DN (bit 13) • The done bit is set by SQO instruction after it has operated on the last word in the sequencer file. It is reset on the next falseto-true rung transition after the rung goes false.

– Enable EN (bit 15) • The enable bit is set by a false-to-true rung transition and indicates the SQO instruction is enabled.

Electrical & Computer Engineering

Dr. D. J. Jackson Lecture 9-14

9-7

Sequencer Status Bits (continued) • LENGTH – The length is the number of steps of the sequencer file starting at position 1 – The maximum number of words is 255 (in MicroLogix 1000 controllers the maximum is 104 words) – The zero position is the startup position – At the end of each cycle the instruction resets to position 1 (A run time major error will occur if the length value points past the end of the programmed file)

• POSITION – The position is the word location or step the sequencer file from/to which the instruction moves data (A run time major error occurs if the position value points past the end of the programmed file) Electrical & Computer Engineering

Dr. D. J. Jackson Lecture 9-15

Using SQO • This output instruction steps through the sequencer file whose bits have been set to control various output devices • When the rung goes from false-to-true, the instruction increments to the next step (word) in the sequencer file • Data stored there is transferred through a mask to the destination address specified in the instruction • Current data is written to the corresponding destination word every scan that the rung remains true • The done bit is set when the last word of the sequencer file is transferred. On the next false-totrue rung transition, the instruction resets the position to step one Electrical & Computer Engineering

Dr. D. J. Jackson Lecture 9-16

9-8

Using SQO (continued) • If the position is equal to zero at startup, when you switch the processor from the program mode to the run mode instruction operation depends on whether the rung is true or false on the first scan – If true, the instruction transfers the value in step zero – If false, the instruction waits for the first rung transition from false-to-true and transfers the value in step one

• The bits mask data when reset and pass data when set – The instruction will not change the value in the destination word unless you set mask bits

• The mask can be a constant or taken from an address Electrical & Computer Engineering

Dr. D. J. Jackson Lecture 9-17

SQO Example

Electrical & Computer Engineering

Dr. D. J. Jackson Lecture 9-18

9-9

SQC Instruction • Applications of the SQC instruction include machine diagnostics. • SQC FD bit is set when the instruction detects that an input word matches (through mask) its corresponding reference word. • The FD bit R6:21/FD is set in this example, since the input word matches the sequencer reference value using the mask value.

Electrical & Computer Engineering

Dr. D. J. Jackson Lecture 9-19

Sequencer Load (SQL) • The SQL instruction stores 16-bit data into a sequencer load file at each step of sequencer operation. The source of this data can be – an I/O or storage word address, – a file address, – or a constant.

Electrical & Computer Engineering

Dr. D. J. Jackson Lecture 9-20

9-10

SQL Operation

Electrical & Computer Engineering

Dr. D. J. Jackson Lecture 9-21

9-11...