The pullups are provided by the ROW input pins. Recall that the 8051 type pins are quasi-birirectional with on-board weak pullups. Now that said I generally would recommend placing 4.7K ohm resistors on the row inputs if there is a chance of excess noise on the keypad matrix pins or if there is a need for a wiping current for the key switches in the matrix keypad.

When using the shown circuit in a mode to allow for a wakeup interrupt to the CPU the software should place all of the column outputs to a low level output. Upon a key detect interrupt the software can then drive the column outputs high and run a conventional key scan algorithm to determine which switch has been pressed.

Michael Karas