>> Joypad operation

The chip (with the chip-on-board package) inside the Radica controller is the same as a 74HC157 data selector

First, here are the signals going to the controller:

The SEL signal is directly hooked up to the 74HC157's select line. A low on SEL selects the B/Left/Right/C Buttons. A high on SEL selects the A/Start Buttons. The Up/Down/Reset buttons are independent of the SEL signal. All buttons are active low, and pull-ups should be provided to each button in order to present a logic 1 when a button is depressed.

Sega genesist used a little but different approach in joystick connection than Atari. The Sega joytick pinout seems to be the "standard" 2 button joystick configuration where pins 6 and 9 are used for buttons which ground the pin when pressed. The only strange thing is that the joystick seems to want +5V also at pin 5. Sega has added more buttons to it"s newer joystick models (there are 3 and 6 bitton models). Those joysticks use basically the same interface, but more buttons are added by extra electronics which multiplexes the new button signals with the existing joystick signals using control bit in connector pin 7.

The chip inside the controller is a 74HC157. This is a high-speed cmos quad 2-line to 1-line multiplexer. The console can with help of the Select-pin choose from two functions on each input.
9 pin D-SUB male connector at the game