Fully Testable Selector Circuit for a Multiport Latch
Original Publication Date: 1989-May-01
Included in the Prior Art Database: 2005-Jan-27
By means of a priority selector circuit for a multiport latch or register, simultaneous multiple port selection is avoided during testing. This priority selector also allows random pattern (self) testing of multiport circuits. Referring to the figure, port selection inputs 2, 4, 6, and 8 go to three logic gates which assure a port selection signal at only one of output ports 10, 12, 14, or 16. The circuit for port selection inputs 6 and 8 is identical to the circuit for port selection inputs 2 and 4. Input 2 goes through an inverter I into one input of a NOR gate 20 and input 4 is one input to a NAND gate 24. Port select output 10 is the output of NOR 20 and the signal at output port 12 is the inverted output of NAND 24. If additional ports exist in the circuit to be tested, the circuit is repeated as necessary.