CH6 Program control instructions(程序控制命令).ppt

1、Chapter 6 Program control instructions,6-1 the JUMP group 6-2 Controlling the Flow of an assembly language program 6-3 procedures 6-4 introduction to interrupts 6-5 machine control and miscellaneous instructions,6-1The JUMP group,Unconditional jump (JMP) Short jump 1000:0100 JMP 0105 8-bit displacem

2、ent Distance for jump : -128127 Near jump 1000:0100 JMP NEAR 0105 jump within current segment 16-bit /32-bit displacement for 8086/80386 Distance for jump:32K/2G Far jump 1000:0100 JMP FAR 2000:0000 Jump to any location segment : offset address contained in the instructions,6-1The JUMP group,Uncondi

3、tional jump Jump with register operands JMP AX Indirect jump JMP SI JMP BX+100H,6-1The JUMP group,Conditional jumps and conditional sets Above or below For comparing unsigned numbers Carry is tested Greater or less For comparing signed numbers Sign flags is tested,Conditional jump,Example for condit

4、ional jump,MOV AX,1234H MOV BX,1000H CMP AX,BX JG IF_GREATER MOV CX,1 JMP NEXT_1 IF_GREATER:MOV CX,0 NEXT_1: RET,AX=1234H BX=1000H If AXBX CX=0 Else CX=1,6-1The JUMP group,Loop CX is decremented Jumps to the address indicated if CX0 Example: for (CX=10;CX=0;CX-) MOV CX,10; Label1: NOP LOOP Label1 NO

5、P is executed by 10 times.,Loop Loop Loopw Loopd Conditional loop LOOPE loop while equal LOOPNE loop while not equal,6-3 Procedures,Example 6-16 SUMS PROC NEAR ADD AX,BX ADD AX,CX ADD AX,DX RET SUMS ENDP SUMS1 PROC FAR ADD AX,BX ADD AX,CX ADD AX,DX RET SUMS1ENDP,6-3 Procedures,Call instruction Near

6、call Operation Push the offset for next instruction into the stack Add the displacement to IP Call procedures within the segment (32K) Far call Operation Push the segment & offset address for next instruction into the stack Replace CS & IP with segment & offset following the CALL opcode. Call proced

7、ures within the memory space,Call a procedure,Main program,procedure,Stack,CALL 2000H,RET,CS:1003H,CS:2000H,CS:1000H,10H 03H,2000H,IP,Calling,Main program,procedure,Stack,CALL 2000H,RET,CS:1003H,CS:2000H,CS:1000H,10H 03H,1003H,IP,CS:2100H,Returning,Figure 6-6 the effect of the near call on the stack

8、 and the instruction pointer,SP before CALL =FFFF SS before CALL =A000 IP before CALL =0003 CS=1000,Figure 6-7 the effect of a far CALL instruction,SP before CALL =FFFF SS before CALL =A000 IP before CALL =0005 CS=1000,CALL with register operand CALL BX CALL with indirect Memory Address CALL BX,RET

9、instruction,RET (near return ) Return from procedure called by near call 16-bit number is removed from the stack to replace IP RETF (far return) Return from procedure called by far call 32-bit number is removed from the stack to replace CS & IP RET n Remove offset address from the stack and extra by

10、tes from the stack,6-4 introduction to interrupts,Interrupt Interrupt service routine is called when interrupt event occurs Interrupt event Hardware interrupt Internal interrupt (exception) Software interrupt,Interrupt,Main program,# 10 interrupt service procedure,Stack,mov ax,3,IRET,CS:1003H,1000H:

11、2000H,CS:1000H,FLAG 0100H 1003H,1000H,IP,interrupt,add ax,bx,1000H 2000H,#10 interrupt vector,0100H,CS,#10 interrupt request,Main program,# 10 interrupt service procedure,Stack,mov ax,3,IRET,CS:1003H,1000H:2000H,CS:1000H,FLAG 0100H 1003H,1000H,IP,returning,add ax,bx,1000H 2000H,#10 interrupt vector,

12、0100H,CS,6-4 introduction to interrupts,Interrupt vectors A table starts from 00000H with 1024 bytes,20H,00H,23H,ABH,10H,00H,12H,34H,00000H,00001H,00002H,00003H,00004H,00005H,00006H,00007H,00008H,00009H,0000AH,0000BH,#0 1000H:1234H,#1 2000H:23ABH,003FFH,003FEH,003FDH,003FCH,#0FFH (255),#2,INT s IRET/IRETD INT 3 INTO,Interrupt service