Multiplex Drive (1/2, 1/3, 1/4)
Segments share rows and columns of drive lines, letting far more of them be controlled from far fewer connections.
What It Is
Multiplex drive organizes segments into a grid of shared row and column drive lines -- described by a ratio like 1/2, 1/3 or 1/4 -- so a controller can address many more segments than it has physical pins for.
How It Works
Instead of one dedicated connection per segment, groups of segments share common lines, and the driver cycles through rows fast enough that the human eye perceives them as being on continuously (the same principle as scanning a matrix keypad or LED display). A 1/3 multiplex ratio, for example, drives the panel in three time-sliced passes per refresh cycle, letting one set of drive lines control roughly three times as many segments as a static (1/1) scheme could with the same pin count. Higher ratios (1/4 and beyond) pack in still more segments, at the cost of needing a display technology -- typically STN or FSTN -- with a steep enough electro-optic response to keep contrast clean at that ratio.
Pros
- Dramatically fewer connections needed for a given segment count
- Scales to the high segment/icon counts complex panels need
- Standard, well-supported driving scheme with widely available driver ICs
Cons
- Needs a display technology (STN/FSTN) suited to the chosen multiplex ratio to avoid contrast loss
- Slightly more complex driving circuitry and timing than static drive
Best For
Multi-digit, icon-dense panels -- the same energy meters, data loggers and instrument clusters that call for STN or FSTN technology -- where pin count has to stay manageable.
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