This is My 4 Bit computer with 6 instructions just like the SAP Computer. :)

Instructions:

00 NOP

1x LDA

2x ADD

3x SUB

ee OUT

4x OUT_S

ff END

Warning:

This computer cannot calculate more than 2 numbers

This Example Program shows 5+7 and 4-5.

To Program, Set the Reset Bit to 1 and Program the ROM.

To Run the Program, Set the Reset Bit to 0.

The Numbers in the output are in Two's Complement so if the number is more than 7 

than the number will be negative because 7 is the biggest number in 4 bits.