One position is unused in the 64-channel variant. In operation each column line is, in turn, set
to a logic low level. As each column is scanned the row lines are read by the port 0 lines to
determine if any keys on that particular column have been pressed. This occurs for each of
the three rows and the control program is then able to determine which key has been pressed
and what action to take. When a pressed key is detected it is debounced by reading the matrix
a number of times to ensure that only one key press is registered. Some keys have been
designated as auto-repeating keys, in which case once the auto-repeat sequence has been
entered the matrix will be read at the auto repetition rate.
Section 3 Page 28
