The 8253 timer is used to generate transmit and receive clock for serial. In addition the CURSOR output of the CRTC is connected as a trigger which is then connected to the colour hardware. So the CRTC cursor can be used to switch colours by the hardware.
Aleste ROM is 64KB, additional :* page have 0 is modified Amstrad CPC6128 OS ROM* page 1 is Amstrad BASIC* page 2 is AMSDOS (Amstrad DOS)* page 3 is Boot Rom, BIOS SETUP and Setup, MSXDOS Boot Loader.boot loader
The BIOS SETUP lets control over: date and time, boot drive, RAM disk, screen mode and style, printer, serial port, and mouse.