Glue logic

Inelectronics,glue logicis the customlogic circuitryused to interface a number ofoff-the-shelfintegrated circuits.This is often achieved using common, inexpensive7400- or4000-series components. In more complex cases, aprogrammable logic devicelike aCPLDorFPGAmight be used. The falling price of programmable logic devices, combined with their reduced size and power consumption compared to discrete components, is making them common even for simple systems. In addition, programmable logic can be used to hide the exact function of a circuit, in order to prevent a product from beingclonedor counterfeited.

The software equivalent of glue logic is calledglue code.

Usage

Typical functions of glue logic include:

• Simple logic functions.
• Address decoding circuitryused with older processors like theMOS Technology 6502orZilog Z80to divide up the processor's address space into RAM, ROM and I/O. Newer versions of these processors, such as theWDC 65816or theZilog eZ80,may add features that enable glueless interfacing to external devices.
• Buffers to protect outputs from overload, or protect sensitive inputs fromelectrostatic dischargedamage.
• Voltage level conversion,e.g.,when interfacing one logic family (CMOS) to another (TTL).

See also

• Glue code
• Reverse engineering