Servicing Personal Computers, 3rd Edition

60 Servicing Personal Computers

A simple 8x8 keyboard matrix and associated inverting buffers/drivers is shown in Figure

1.66. The keyboard rows are driven by the eight least significant address lines, AO to A7. The

keyboard columns provide inputs to the system data t>us, DO to D7. A common enable signal

is fed to the keyboard data bus buffers. This signal, KB, is derived from the address decoding

logic such that the keyboard becomes enabled when the most significant address bits take the

following pattern:

A15 A14 A13 A12 A11 A10 A9 A8

0 0 1 1 10 0 0

The remaining address bits, A0 to A7, are scanned under software control such that only

on ...