# IEC bidirectional (universal) shift register Canonical URL: https://eloragrid.ai/symbols/iec-bidirectional-shift-register Publisher: Elora Grid Updated: 2026-10-28 Lookup label: SRG4 Drawing use: Schematic Reference families: IEC, Manufacturer ## Symbol convention Convention: IEC Form: SRGm element with mode inputs selecting shift right, shift left and parallel load Qualifying-symbol and dependency conventions as explained in TI's public overview of IEEE Std 91-1984, which incorporates IEC 617-12 work. Independent educational drawing; not certified IEC geometry or an IEC database identifier. IEC shift register with mode inputs that select shift right, shift left, parallel load or hold. ## In plain English ### What does IEC bidirectional (universal) shift register mean? A universal shift register is drawn as an SRG element with two mode-select inputs grouped to produce modes 0 to 3. The clock label shows shift right under one mode and shift left under another, while data inputs are labelled with their mode and control numbers, such as 1,4D for serial right input and 3,4D for parallel load. ### A simple example These devices are used in data conversion, sequence generation and bidirectional serial links. Reading the compound labels left to right, mode first then clock, tells you exactly when each input is used. ### What the drawings help you do The symbol does not state which mode is safe to change during clocking. Mode changes are normally made with the clock inactive. ### This particular reference IEC shift register with mode inputs that select shift right, shift left, parallel load or hold. A single-direction SRG register has no mode inputs and shifts only one way. ### Terms - Signal: Electrical information passed between devices, rather than necessarily the main power supply. - Schematic: A drawing showing function and connections rather than physical appearance. Concept diagram: Identify the device and form → Read the connections and state → Check the equipment reference A guide to reading this reference. The original symbol illustration and its drawing notes appear below; these boxes are not a wiring diagram. - [Overview of IEEE Standard 91-1984: explanation of logic symbols (SDYZ001A)](https://www.ti.com/lit/ml/sdyz001a/sdyz001a.pdf) ## What it represents A universal shift register is drawn as an SRG element with two mode-select inputs grouped to produce modes 0 to 3. The clock label shows shift right under one mode and shift left under another, while data inputs are labelled with their mode and control numbers, such as 1,4D for serial right input and 3,4D for parallel load. These devices are used in data conversion, sequence generation and bidirectional serial links. Reading the compound labels left to right, mode first then clock, tells you exactly when each input is used. The symbol does not state which mode is safe to change during clocking. Mode changes are normally made with the clock inactive. ## How to read it - Decode the mode inputs first. - Compound labels such as 1,4D give mode then clock. ## Information to show or reference - Show the mode-select grouping. - Label both shift directions on the clock. - Label serial and parallel data inputs with their mode numbers. ## Important distinction A single-direction SRG register has no mode inputs and shifts only one way. ## Facts - Modes: Hold, shift right, shift left, parallel load - Notation: M dependency with shift arrows - Artwork scope: Original educational illustration; consult the applicable standard and the selected device documentation for the exact graphic ## Public references - [Overview of IEEE Standard 91-1984: explanation of logic symbols (SDYZ001A)](https://www.ti.com/lit/ml/sdyz001a/sdyz001a.pdf) — Texas Instruments. Shift right and left labels and M dependency examples. ## Graphic scope Independent original educational concept illustration by Elora Grid. Not a certified standards graphic or manufacturer footprint. Unitless; not to scale. Original artwork licence: https://creativecommons.org/licenses/by/4.0/. Publisher material is linked only.