Following up a post from MSX Resource Center, I can think of an adapter to connect the Atari Keyboard Controller adapter on the MSX.

The keyboard can be read by pulling down consecutively the pins 6, 7, and 8 of the joystick port, while keeping the other pins at high, and read the key pressed on the directionals. A key pressed will appear as LOW.

The diode on pin 8 is to simulate an open collector thus preventing a combination of bad code an many keys pressed at the same time. The pins 6, and 7 are already open collectors and does not require the diode.

The external 4k7 resistor may not be necessary,

Just the adapter: