The upper nibble of the requested ROW (or AND of row data as directed by KD4) is sent from the keyboard to the main unit. D0 = AND of bit 0 on ROWS 0 to 13, D1 = AND of bit 1 on ROWS 0 to 13 etc. The keyboard must return a logical AND of all the keys, ie. The keyboard must return the actual key matrix data as referenced by the Row number. The keyboard is transmitting requested data over the 4 bit bidirectional bus KD.
KD is a bidirectional bus between the main unit and the keyboard, direction under main unit control using RTSN.Ī Row address is being transmitted from the main unit to the keyboard. RTSN, KD4, MPX are output signals from the main unit side.
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