Original Gatearray of Amstrad is a sequencer, it manage synchronization between video card and z80 and memory access.
Historically they there are a link between CU of CU/ALU, and... control bus and... making a own sequencer. But I will say more in order to not disturb these text part xD
Whatever, I made my own sequencer here in form of a bus of 4 wires called CLK4. CLK4 execute a simple repetitive sequence like 0001 0010 0011... CLK4(3), the last wire is directly connected to Z80 clock entry. Component not using explicit CLK4 as clock entry are generally using a not(CLK4(3)) entry, in order to do operation not as same time than z80.