Shift register (LOGO! 8.FS4 and later versions only)

Short description

The shift register function reads an input value and shifts the bits. The output value corresponds with the configured shift register bit. The shift direction can be changed at a special input.

For LOGO! 8.FS4 devices, you can use a maximum of four shift registers with eight bits for each shift register in one circuit program.

Connection

Description

Input In

The function when started reads this input value.

Input Trg

The SFB is started with a positive edge (0 to 1 transition) at input Trg (Trigger). A 1 to 0 transition is irrelevant.

Input Dir

You define the shift direction of the shift register bits Sx.1 to Sx.8 at the Dir input:

Dir = 0: shift up (Sx.1 >> Sx.8)
Dir = 1: shift down (Sx.8 >> Sx.1)

NOTE:

"x" refers to the index of the shift register.

Input R

The SFB is reset with a positive edge (0 to 1 transition) at input R (Reset). When the SFB is reset, all the shift register bit (Sx.1 to Sx.8) and the output at Q are set to 0.

Parameter

Shift register index: the index of shift register in the circuit program.

Possible settings: 1 to 4

Shift register bit that determines the value of output Q.
Possible settings: 1 to 8

Retentivity set (on) = the status is retentive in memory.

Output Q

The output value corresponds with the configured shift register bit.

Parameter

LOGO! 8.FS4 devices provide four shift registers, with eight bits for each shift register. The shift register index corresponds to one of the four shift registers in the circuit program. The shift register bits are numbered in Sx.y, in which x is the index, and y is the bit number.

Timing diagram

If the shift register index is 1, the shift register bits will be S1.1 to S1.8.

Description of the function

The function reads the value of input In with a positive edge (0 to 1 transition) at input Trg (Trigger).

This value is written to shift register bits Sx.1 to Sx.8, depending on the set shift direction:

A positive edge (0 to 1 transition) at input R (Reset) reset the shift register. All the shift register bit (Sx.1 to Sx.8) and the output at Q are set to 0.

Q outputs the value of the configured shift register bits.

If retentivity is not enabled, the shift function restarts at Sx.1 or Sx.8 after a power failure.

Special functions