SAN3010

The SAN3010 interface must be capable of forcing the keyboard rows (hereafter indicated as R1...R4) both low (Vss) and high (VDD) and forcing the keyboard columns (hereafter indicated as C1...C4) to high (VDD). Only one row or column is forced at the same time while the remaining rows/columns must be high ohmic (hereafter indicated as Hi Z). Since only one row/column must be driven at the same time, a decoder (IC5 = 74138) was implemented to save pin count of the C. 3 output ports were used for row/column selection, 1 output port to disable all rows/columns and 1 output port for the 3-state buffer inputs to select forcing high or low . One SAN3010 C pin must be configured as input for handshake.

If 9 output + 1 input pins SAN3010 are available from the C (8 row/column selectors, 1 force hi/lo selector , 1 handshake input) , IC5 = 74138 can be omitted.

IC3 & 4 (=74HC125) are separately addressable 3-state buffers.

A simple discrete NOR gate (Q1,D2,D3,R9..11) is used for synchronization.