Write a symbolic microprogram routine for the ISZ (increment and skip if zero) instruction defined in Chap. 5 (Table 5-4). Use the microinstruction format of Sec. 7-3. Note that DR = 0 status condition is not available in the CD field of the computer defined in Sec. 7-3. However, you can exchange AC and DR and check if AC =0 with the Z bit.

Table 5-4

Symbol AND ADD LDA STA BUN BSA ISZ TABLE 5-4 Memory-Reference Instructions Operation decoder Do D D6 Symbolic description AC AC A M[AR] AC AC + M[AR], E-Cout AC+M[AR] M[AR] AC PC-AR M[AR] PC, PC AR + 1 M[AR] M[AR] + 1, If M[AR] +1=0 then PC-PC + 1