SRG4
IEC bidirectional (universal) shift register
IEC shift register with mode inputs that select shift right, shift left, parallel load or hold.
IEC
IEC · Mm
IEC mode dependency (M)
Dependency label Mm used to show operating modes; affected inputs and outputs act only in the selected mode.
In plain English
What does IEC mode dependency (M) mean?
M dependency is used where a device has several operating modes. When an Mm input is at its internal 1 state, inputs and outputs labelled m have their normal effect; otherwise they are disabled. Mode inputs are often produced from two select lines by binary grouping, giving M0 to M3.
A simple example
Universal shift registers and up/down counters are typical users. On the symbol, a label such as 1,4D means the input acts as data only in mode 1 and with control 4. Reading these compound labels from left to right gives the order of conditions.
What the drawings help you do
The notation does not define what happens during a mode change. Any restrictions on changing mode while clocking are device-specific.
This particular reference
Dependency label Mm used to show operating modes; affected inputs and outputs act only in the selected mode. A (address) dependency selects among arrays of identical elements; M selects operating modes of one element.
- Signal
- Electrical information passed between devices, rather than necessarily the main power supply.
- Rating
- A value stating the conditions for which equipment is specified.
- Schematic
- A drawing showing function and connections rather than physical appearance.
Read the source: Overview of IEEE Standard 91-1984: explanation of logic symbols (SDYZ001A)
IEC · Mode inputs labelled Mm, often produced by binary grouping, with affected terminals labelled m
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.
Shown as an independently authored educational illustration. Use the cited publication and drawing legend to verify the required drafting form.
Schematic · Mm
What it represents
M dependency is used where a device has several operating modes. When an Mm input is at its internal 1 state, inputs and outputs labelled m have their normal effect; otherwise they are disabled. Mode inputs are often produced from two select lines by binary grouping, giving M0 to M3.
Universal shift registers and up/down counters are typical users. On the symbol, a label such as 1,4D means the input acts as data only in mode 1 and with control 4. Reading these compound labels from left to right gives the order of conditions.
The notation does not define what happens during a mode change. Any restrictions on changing mode while clocking are device-specific.
How to read it
- Decode the mode inputs before reading other labels.
- Compound labels list affecting numbers separated by commas.
Information to show or reference
- Show the mode-select inputs and their binary grouping.
- Label affected terminals with the mode numbers.
- Tabulate the modes in a note if the symbol is complex.
A distinction that matters
A (address) dependency selects among arrays of identical elements; M selects operating modes of one element.
Sources you can follow
These public references support the explanation and provide further detail. Their graphics and downloadable files remain with their publishers.
Overview of IEEE Standard 91-1984: explanation of logic symbols (SDYZ001A)
M (mode) dependency affecting inputs and outputs.
About this graphic
This illustration was authored independently by Elora Grid to explain the concept. It is not reproduced from a customer drawing, an official standard graphic or a manufacturer CAD file. Its correspondence to an exact IEC or IEEE symbol identifier has not been certified.
SVG and DXF downloads contain this original artwork. DXF uses unscaled drawing units; a GA envelope supplies no product dimensions, clearances or fabrication information. Original artwork is available under CC BY 4.0. Third-party references retain their own terms.
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