Question

SUBROUTINES Example 2: May 2006 Question 2 The main program uses a subroutine located at address 3000,- Read the program and answer the following questions. (a) What is the address of the instruction DCR E in the main program?[3 marks] (b) What instructions need to be written in the subroutine and give the address of the instructions? [3 marks] List the contents of the stack, the PC, and the stack pointer after (i) Execution of CALL instruction in the main program. [5 marks] (ii) Execution of instruction PUSH PSW in the subroutine. [9 marks] Address Main Program Address Subroutine 2000 LXI SP, 2100 3000 PUSH H LXIH,00A8 PUSH D MVI E, 5D PUSH PSW CALL 3000 MVI B, OD LXIH, FF00 DCRE 3010 RET 16

Answer 1

[2.] Maior poogalom. Address Hey Mone anonic code opcode LXI SP, 2100 Stacle Poin dey pointed To 2100 2001 00 21 2002 003 Opcode LXIH, DOAS! dati 0 HL pery -0018 stic inter L 2 CALL 2004 AS 2005 oo 2006 Opcode MV ESD E per. - SD data of o opCode MVIE SD 2007 SD 2008 opcode CALL 3000. After cell instrction 2009 200B PUSH ion to 200 A stick pointer per 20013 DOR E and pc pointeals to 3000H Address subroutine Memory of 8085 3000 PUSH H Sp) 2100 X X - 3001 PUSH D 2. OFF! 20H 2002 PUSH P5W Alpe =207€ OBH - MUEB, OD 2 of oo ?Pust -3005 LXIF FOO 2 of cl A8 2 Push 20FAL SD 300D POP psw 20F9 rosho ?PUSH 300 E Pop D dut of TIpsw 2018 LAURI 300 F POP H cs Scanned with 30 scanner ET 3000 3003 2018 detto! After PUSHPSW Stoic ponki

(9.) The The address of the instreton DCRE in the main progasm is 200BH add . (6) In the subroutine from 3008 to 300 e ang infection we can write except any jump, Cell, Push or pop instion instruction. After thet pop psw, Popo, poph 3008 --.. 2 Any joshecim 3ooc Tex Capt, PUSH, PoP, Tuorp, call, RET 300D pop powo 3ooE Pop » 300 E pop H 3010 RET (6) Executim of C ALL instruction, in the main program, the steel pointer = 20 FE content of stick pointer 0314 - PC = 30004 i Execution of instruction PUSH Psw in the subrouting strek pointer = 2018 contents of Steel pointers contents of PC -30034 flag Reg. Scanned with CamScanner