MODE (mod) FIELD CODES. mod MEMORY MODE: 8-BIT DISPLACEMENT MEMORY MODE: 16- OR 32- BIT DISPLACEMENT REGISTER MODE

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5 EXERCISE 9. Determine the mod bits from Figure 7-24 and write them in Table 7-7. MODE (mod) FIELD CODES mod DESCRIPTION MEMORY MODE: NO DISPLACEMENT FOLLOWS MEMORY MODE: 8-BIT DISPLACEMENT MEMORY MODE: 16- OR 32- BIT DISPLACEMENT REGISTER MODE NOTE: WHEN r/m EQUALS 110. THERE IS A 1 6-BIT DISPLACEMENT. Figure Determine the reg bits from Figure 7-25 and write them in Table 7-7. REGISTERS SPECIFIED BY REG (reg) FIELD reg OR 32- BIT DATA OPERATION AL CL DL AH CH BH 16- BIT DATA OPERATION w = l AX CX SP BP I 32- BIT DATA OPERATION w = l o r n o w f i e l d ECX EDX EBX ESP ESI Figure You now have the binary value for the first nibble of the second byte. Write the hex value below the binary value in Table Determine the r/m bit from Figure 7-26 and write it in Table BIT ADDRESSING EFFECTIVE ADDRESSES SPECIFIED BY r/m AND mod FIELDS r/m = [Bx [BX SI d8] Figure 7-26 [SI d 1 [Bx d 1 6 ] 13. You now have the binary value for the second nibble of the second byte. Write the hex value below the binary value in Table 7-7.

6 Instruction Formats - II 14. What is the hex displacement value in the instruction MOV CX,[BX SI 0060H]? 15. For the displacement 0060H, what hex code follows the first two bytes 8B 88? 16. What is the complete instruction code for the mnemonic MOV CX,[BX SI 0060H]? 17. To test the instruction code for the mnemonic MOV CX,[BX SI 0060H], do the following on the 32-BIT MICROPROCESSOR circuit board. 1. Turn the SINGLE CYCLE switch to OFF and press RESET. 2. Enter "0200" in the CS register. 3. Enter "1000" in the IP register. 4. Enter "01 00" in the DS register. 5. Enter a base value "3000" in the BX register. 6. Enter an index value "0004" in the SI register. With a base value of 3000, an index value of 0004, and a displacement of 0060, what is the EA? 18. Continue by entering the memory operand and instruction code. 1. Press <EXIT> and then press <READ>. 2. Enter the logical address " " for the memory operand. 3. Starting at address 04064, enter "88 77" for the operand, which is Press <READ> and enter the logical address " " for the instruction code. 5. Starting at address 03000, enter the instruction code "8B ". 6. Press <STEP> to execute the instruction code.

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9 EXERCISE 29. You now have the binary value for the second nibble of the second byte. Write the hex value below the binary value in Table Determine the mod bits from Figure 7-28 and write it in Table 7-8. MODE (mod) FIELD CODES mod DESCRIPTION MEMORY MODE: NO DISPLACEMENT FOLLOWS * MEMORY MODE: 8-BIT DISPLACEMENT MEMORY MODE: 16- OR 32-BIT DISPLACEMENT REGISTER MODE * NOTE: WHEN r/m EQUALS 110. THERE IS A 16-BIT DISPLACEMENT. Figure 7-28 Determine the reg bits from Figure 7-29 and write it in Table 7-8. REGISTERS SPECIFIED BY REG (reg) FIELD 16- OR 32- BIT DATA OPERATION w = O AL CL DL BL AH CH DH BH 16-BIT DATA OPERATION w = l or no w field AX CX DX BX SP BP SI Dl 32-BIT DATA OPERATION w = l or no w field EAX ECX EDX EBX ESP EBP ESI EDI Figure You now have the binary value for the first nibble of the third byte. Write the hex value below the binary value in Table Determine the r/m bits from Figure 7-30 and write it in Table BIT ADDRESSING EFFECTIVE ADDRESSES SPECIFIED BY r/m AND mod FIELDS Figure You now have the binary value for the second nibble of the third byte. Write the hex value below the binary value in Table 7-8.

10 InstructionFormats- II 35. The scaled index (EDI*2)is given in the mnemonic. Determine the ss bits from Figure 7-31 and write them in Table 7-8. SS FIELD IN S-I-B BYTE ss SCALE FACTOR Figure Determine the index bits from Figure 7-32 and write them in Table 7-8. INDEX (index) FIELD IN S-1-B BYTE SPECIFIED BY INDEX REGISTER index *NOTE: WHEN THE INDEX FIELD IS 100. THEN THE SS FIELD MUST EQUAL 00. Figure 7-32 INDEX REGISTER EAX ECX EDX EBX NO INDEX REG* EBP ESI EDI Determine the base bits from Figure 7-33 and write them in Table 7-8. BASE (base) FIELD IN S-1-B BYTE SPECIFIED BY EFFECTIVE ADDRESS base mod = 01 mod = [EDX d8] [ECX [EDX d8] [ESP d8] [EBP d8] [EAX (S*l) [ECX [EDX [EBX [ESP [EBP NOTE: S*l EQUALS THE SCALING FACTOR TIMES THE INDEX VALUE. Figure You now have the binary value for the last instruction byte. Write the hex value below the binary value in Table What is the complete instruction code for the mnemonic MOV [ECX (ED l*2)], BX?

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13 EXERCISE 7- For the instruction MOV EBX,[ECX (EDI*4) 0520F8AB], what are the r/m field bits? 32- BIT ADDRESSING EFFECTIVE ADDRESSES SPECIFIED BY r/m AND mod FIELDS r /m mod = 00 mod = 01 mod = [EAX] [ E C X ] [ E D X ] [ E B X ] s- i- b present d32 [ E S I ] [ EDI] [EAX d8] [ECX d 8 ] [EDX d 8 ] [EBX d 8 ] s-i-b present [EBP db] [ESI db] [EDI d8] [EAX d32] [ECX d32] [EDX d32] [EBX d32] s- i- b present [EBP d32] [ESI d32] [EDI d32] Figure 7-36 For the instruction MOV EBX,[ECX (EDI*4) 0520F8AB], what are the index field bits? INDEX (index) FIELD IN S-1-B BYTE SPECIFIED BY INDCX REGISTER index INDEX REGISTER EAX ECX EDX EBX NO INDEX REG* EBP ESI ED1 *NOTE: WHEN THE INDEX FIELD IS 100. THEN THE SS FIELD MUST EQUAL 00. Figure 7-37

14 Instruction Formats- II BASE (base) FIELD IN BYTE SPECIFIED BY EFFECTIVE ADDRESS base m o d = 00 m o d = 01 mod = [EAX (S*I)] [EAX (S*l) db] [EAX (S*l) d32] 001 [ECX (S*I)] [ECX (S*I) db] [ECX (S*l) d 3 2 ] 010 [EDx (S*I)] [EDX (S*I) d8] [EDX ( S * I ) d32] 011 [EBx (S*l)] [EBX (S*I) d8] [EBX (S*I) d32] [ESP (S*l)] [d32 (S*I)] [ESl (S*I)] [ESP (S*I) d8] [EBP (S*I) d8] [ESI (S*I) d8] [ESP (S*I) d32] [EBP (S*I) t d32] [ESl (S*I) d32] [ED1 (S*l)] [ED1 (S*I) d8] [ED1 (S*I) d32] NOTE: S'I EQUALS THE SCALING FACTOR TIMES THE INDEX VALUE. Figure For the instruction MOV [ESl (EDX*8)],EAX, what are the base field bits?