Uncommitted Logic Array

Encyclopedia : U : UN : UNC : Uncommitted Logic Array

An Uncommitted Logic Array (ULA) is a silicon chip whose surface has a two-dimensional array of simple logic elements such as NAND or NOR gates. A final surface layer of metal interconnections is then deposited to join these elements to form more complex functions. This layer is analogous to the copper layer of a single-sided printed circuit board PCB.

This allowed companies to commission their own chip designs without having to do so from scratch. The underlying ULA chip was already there, so only the single connection layer had to be designed. This is much cheaper than developing a full-custom chip design.

Sinclair Research ported an enhanced ZX80 design to a ULA chip for the ZX81, and later used a ULA in the ZX Spectrum.

Acorn Computers used several ULA chips in the BBC Micro, and later managed to compress almost all of that machine's logic into a single ULA for the Acorn Electron.

Many other manufacturers from the time of the home computer boom period used ULAs in their machines.

Ferranti in the UK pioneered ULA technology, then later abandoned this lead in semi-custom chips. The IBM PC took over the computer market, and the sales volumes made full-custom chips more economical.

Designers still wished for a way to create their own complex chips without the expense of full-custom design, and eventually this wish was granted with the arrival of Field-Programmable Gate Array (FPGA) chips. Whereas a ULA required a semiconductor wafer foundry to deposit and etch the interconnections, the FPGA had programmable interconnections.

From Wikipedia, the Free Encyclopedia. Original article here. Support Wikipedia by contributing or donating.
All text is available under the terms of the GNU Free Documentation License See Wikipedia Copyrights for details.