On the RTSN falling edge (RTSN goes inactive LOW), MPX goes HIGH for 320ns and the upper nibble of the data set for retrieval is output by the keyboard on KD after 20ns from the MPX rising edge.KD4 is sampled, when LOW the logical AND of all keys per column is set for retrieval, when HIGH the actual column of the selected row is set for retrieval.KD4 state (or state change) precedes the rising edge of RTSN, generally changes on the falling edge prior to the triggering active edge of RTSN. The scan row is read by the keyboard in the remaining 920ns from KD.The mainboard sends a scan row to the keyboard which becomes valid 160ns after the rising edge of RTSN.Thereafter the period is a uniform 660ns active HIGH and 680ns inactive LOW. The initial RTSN period, after detection of a key via STROBEALL, is 1.08us active HIGH and 660ns inactive LOW. RTSN goes active HIGH and remains active for 1.08us.
There are two main modes of operation, a test all (STROBEALL) keys mode, used whilst waiting for a key to be pressed which is followed on by a manual scan of all rows to retrieve column data to locate the pressed key.įor key data retrieval the protocol is as follows: The lower nibble of the requested ROW (or AND of row data as directed by KD4) is sent from the keyboard to the main unit.Īctive when RTSN = HIGH ( 1), transmits the 4 bit row number of the row data from the keyboard matrix.Īctive when RTSN = LOW ( 0), transmits 4 bits of the 8 bit column data of the requested row. 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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