of the Z80 clock input to stop all microprocessor activity. While this is less elegant than performing a bus request, it does gain contended memory access to fewer Z80 clocks. This removes any need for the ULA to read display data in advance, a benefit with the crowded circuitry in the full ULA. The ULA connects directly to the memory system ICs while the Z80 connects to them through isolating series current-limit resistors. This allows the ULA and memory to drive each other while the Z80 is also driving the memory. Using resistors instead of tristate bus driver ICs reduces the expense of the circuit but does take a higher average I/O pin current from the Z80, ULA and memory ICs. References External links Contended Memory on Sinclair FAQ Wiki Contended Memory on worldofspectrum.org Contended Memory on zxdesign.info ZX Spectrum