Since IBM had patented their keyboard design, Amstrad developed an entirely different keyboard.
The Amstrad keyboard is entirely incompatible with XT and AT keyboards, and can be used only on an Amstrad; conversely, no other keyboard will work on an older Amstrad. This keyboard has a Del key on the keypad, and both Del-> and Del<- keys above the Enter key. The Del-> key has scancode 70. Left of the Enter key a PrtSc/* key. There is an additional Enter key with scancode 74. It is possible to connect a mouse and/or joystick to the keyboard, and then these devices also yield scancodes: 77 (joystick button 1), 78 (joystick button 2), 79 (joystick right), 7a (joystick left), 7b (joystick up), 7c (joystick down), 7d (mouse right), 7e (mouse left).
John Elliott adds: The above only mentions the PC1512/PC1640 style of keyboard. Later Amstrad XTs (PPC512, PPC640, PC20, PC200, PC2086, PC3086) used a 102-key keyboard with the same layout and scancodes as a normal 102-key XT keyboard. This design is not only incompatible with normal XT and AT keyboards, it's also incompatible with the PC1512 keyboard. The joystick socket is no longer present, but mouse button clicks are still handled by the keyboard, with the same scancodes 7d (right button) and 7e (left button).
On the PPC512, PPC640, PC20 and PC200, the keyboard is in the same box as the motherboard, and is connected directly to it by ribbon cable.