ECT 464

1. ECT 464 Lecture 17 Shift Registers

2. Today’s Quote: The grass may look greener on the other side, but it still has to be mowed. Keep your lives free from the love of money and be content with what you have, because God has said,    "Never will I leave you;       never will I forsake you." Hebrews 13:5

3. Shift Register Instructions • FFL FIFO Load • FFU FIFO Unload • LFL LIFO Load • LFU LIFO Unload • The FIFO is a First In First Out Register used to buffer data. • The LIFO is a Last In First Out Register used as a stack

4. FIFO Load (FFL) • On a false-to-true rung transition, the FFL instruction loads words into a user-created file called a FIFO stack. This instruction’s counterpart, FIFO unload (FFU), is paired with a given FFL instruction to remove elements from the FIFO stack.

5. FIFO Unload (FFU) • On a false-to-true rung transition, the FFU instruction unloads words from a user-created file called a FIFO stack. The data is unloaded using first-in, first-out order. After the unload completes, the data in the stack is shifted one element toward the top of the stack and the last element is zeroed out.

6. LIFO Load (LFL) • On a false-to-true rung transition, the LFL instruction loads words into a user-created file called a LIFO stack. This instruction’s counterpart, LIFO unload (LFU), is paired with a given LFL instruction to remove elements from the LIFO stack.

7. LIFO Unload (LFU) • On a false-to-true rung transition, the LFU instruction unloads words or long words from a user-created file called a LIFO stack. The data is unloaded using last-in, first-out order.