ZX-81 custom chip - watizit?

On Jul 30, 21:54, Richard A. Cini, Jr. wrote: ZX truly No, it's a ULA (uncomitted logic array, a sort of early ASIC) made by Ferranti. The ULA replaces several TTL chips that were present in the ZX80. There were two or three revisions of these, and a similar idea was used in the Sinclair Spectrum. The BBC Micro also used Ferranti ULAs, one for the serial controller and one for the video controller. IIRC, the ZX and Spectrum ULAs are still available from CPC in Britain. A ULA consists of lots of simple logic gates laid out in a square array, but the basic design has no final metalisation layer - and hence no interconnections between the gates. A designer using a ULA would translate his circuit diagram into an interconnection diagram for the array, and hand that over to Ferranti, who would then produce the mask for the final stage of the manufacturing process. The end result is a bit like an FPGA, but with simopler building blocks. Apart from that, the relationhip between a ULA and an FPGA is bit like the relationship between a masked ROM and an EPROM. -- Pete Peter Turnbull Dept. of Computer Science University of York