Bread80Flags and branch control. This is a nice, easy to understand circuit. It starts with computing the zero, sign and parity flags. Since we have a 1-bit ALU the sign and parity flags are re-evaluated for each bit. Sign flag is just bit 7 of the result. Carry flag circuit is on another page.
IRn are raw bits of the opcode from the instruction register. A multiplexer IC uses IR3 and 4 select a flag to test. IR5 selects for condition true or condition false.