The !CK signal, sometimes referred to as PHICPU is available on Lower Pin 8. This clock signal is generated by the [[The Spectrum ULA|ULA]] and is interrupted during [[contended memory]] access
. This clock signal is inverted by a transistor switch to provide a clean clock edge for the Z80.
This signal is '''NOT''' connected on the [[Investronica]] [[ZX Spectrum+ 128K]].