1. SHIFT REGISTERS A number of internal relays are grouped together to form a register. Provides storage area for a series sequence of individual bits. A 4-bit register can be formed using 4 internal relays, an 8-bit using 8. The bits can be shifted along by one bit when there is a suitable input to the register. (ex) initially an 8- bit register might have: then there is an input of a 0 shift pulse: 0 1 with the result that all the bits shift along one place and the last bit overflows. 10110101 01011010

2. INPUTS TO SHIFT REGISTERS Three inputs 1.To load data into the first element of the register (OUT) - a logic level 0 or 1 is loaded into the first element of the shift register. 2. As the shift command(SFT) – a pulse moves the contents of the register along one bit at a time, the final bit overflowing and being lost. 3. For resetting(RST) – a pulse of a closure of a contact resets the register contents to all 0s.

3. SAMPLE PROGRAM - SHIFT REGISTER StepInstructionNotation 0LDX400 1OUTM140 2LDX401 3SFTM140 4LDX402 5RSTM140 6LDM140 7OUTY430 8LDM141 9OUTY431 10LDM142 11OUTY432 etc. 20LDM147 21OUTY437 Initially 10000000 then 11000000

4. MASTER CONTROLS A whole block of outputs can be simultaneously turned off or on by using the same internal relay contacts in each output rung so that switching it on or off affects every one of the rungs. An alternate way of programming to achieve the same effect is to use a master relay.

5. SAMPLE PROGRAM – MASTER RELAY When there is an input to close input1 contacts, then master relay MC1 is activated and then the block program rungs controlled by the relay follows. MCR - The end of a master relay controlled section. If there is an input to input2, then master relay MC2 is activated and the rungs controlled by that master relay follow. If there are no inputs to both 1 and 2 then the rung that follows in the program is that for input9 controlled output Out6.

6. JUMP CONTROL Used in conditional situations. Enables program to be designed so that if a certain condition exists then a section of the program is jumped. An example is as follows.