The CPC+/GX4000 have two digital joystick ports (which work equivalent to the Y-cable).
== Is this true? ==
Some modification occured in the "Atari" standard
Not problematic most time on a CPC old as ALL oone button joysticks will fit.
But may put some difficulties with the PLUS range.
Amstrad aimed the console market (GX4000) and used some kind of politic of "Exclusive Hardware" (like all console manufacturers of the time).
Not that it was changed compaired to Old CPC generation (yet few CPC games actually supported the 2 button feature, despite available).
And of course the Atari standard was originally a 1 button solution (Atari 8 bit 2600 consoles) but cxould easily be improuved to more buttons.
Sega Megadrives managed easily 6-8 button (Street Fighter 2 standard).
The most notable differences with other consoles using the Atari specs is with Sega systems (Master System and Megadrive) as the Atari standard became Sega standard (most sold console using this standard)
Yet simple re-cabling can be achieved thanks to get a proper adapter made simply :
* a pair of "Atari / 9 pin serial" connectors (one male and one female)
* and simply rewire between both as fit.
This allows to keep the original configuration of Sega compatible Pads/joysticks and benefit from the higher quality level from them.
A clever move too may be to put such converter as a box with wires easily removable/changeable (not soldered, but inserted thank to proper solutions). (A clever move from Amstrad may have been to use SEGA standards).
This would allows to configure more easily different configurations depending on the Game controllers you may find.
*Sega Master system or MegaDrive/Genesis
*Mais even be suitable with Sega LightGuns or Atari/Amiga mouses if you can find a proper Power source and perhaps cables with a bit of electronic composents integrated (diodes, resistors ?).
As a result it may be a problem to find proper Joysticks for your PLUS/GX4000 with benefit from 2nd button, as Sega models won't often fit entirely but are often of a better quality/availability.
Megadrive paddles use Start button as Amstrad fire1 and Button 1 as Amstrad Button 2.
Other noable differences are compaired to Atari ST as the mouse can't fit unless powered.
As a result, different Mouse standards appeared on Amstrad, using Joystick port Or Extension port.
The same goes with lightphaser solutions.
Both could use Joystick port (added power suplly) or Extension port, or even the special LightGun port on Plus range (Is it powered ?).
by adding a power derivation on their Joystick port, Amstrad could have standardised it's technology and ease the CPC community.
== Joystick Related stuff... Sega Controllers... ==