Sequential Pro One - Keyboard;Switch Matrix; Keyboard Receiver Line

2-1 1 KEYBOARDfSW1TCH MATRIX
Looking at the keyboard matrix more closely, the basic scanning operation is to
activate one matrix row of contacts on eight consecutive keys, then check the
intercepting columns for the presence of a bit, The resulting data uniquely identifes a
combination of switch closures in each row. The group of five bytes which represent
the five scanned matrix rows form a "map1' in RAM. By comparing two such maps
made in successive "~cans,~ the computer detects what key($) are being pressed and
released and decides whether to refresh the DAC with a new key number and output
the TRIGGER and GATE,
Actually the matrix harware works on negative logic. To check the first row, U113
outputs the number 1 1110 (1EH) on the data driver. This means pins 5 through 8 are
high, whiie pin 4 (POO) pulls the first row low. The receiver inputs CP10-17) are being
pulled high by internal pull-up resistors, So if no keys in the first row are held, the
receiver inputs the number I111 11 11 (FFH). But suppose key DO is held. This pulls
receiver line PI2 low, so the input number would be 11 11 101 1 IFBW). Figure 2-6 shows
this signal.
~113-20 (~12)
DO HELD
H=5 msfdiv
~=SV /div
Figure 2-16
KEYBOARD RECEIVER LINE