but push-pull, though not likely to go "poof,"
example colums are output, rows are input.
if you push one key from col1 and a key from col2 simultaneously, then col1 and col2 will be shorted. the scan routine will at some time have col1 low and col2 high, i.e. you haqve 2 transistors, both 'on' in series between Vcc and gnd.

Erik