EE 308 Spring 2011 Review Exam 1 • Numbers – Decimal to Hex (signed and unsigned) – Hex to Decimal (signed and unsigned) – Binary to Hex – Hex to Binary – Addition and subtraction of fixed-length hex numbers – Overflow, Carry, Zero, Negative bits of CCR • Programming Model – Internal registers – A, B, (D = AB), X, Y, SP, PC, CCR • Addressing Modes and Effective Addresses – INH, IMM, DIR, EXT, REL, IDX (Not Indexed Indirect) – How to determine effective address • Instructions – What they do - Core Users Guide – What machine code is generated – How many cycles to execute – Effect on CCR – Branch instructions – which to use with signed and which with unsigned • Machine Code – Reverse Assembly • Stack and Stack Pointer – What happens to stack and SP for instructions (e.g., PSHX, JSR) – How the SP is used in getting to and leaving subroutines • Assembly Language – Be able to read and write simple assembly language program – Know basic assembler directives – e.g., equ, dc.b, ds.w Flow chartsEE 308 Spring 2011 Binary, Hex and Decimal Numbers (4-bit representation) Binary Hex Decimal 0000 0001 0010 0011 0100 0101 0110 0111 1000 1001 1010 1011 1100 1101 1110 1111 0 1 2 3 4 5 6 7 8 9 A B C D E F 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Binary to Unsigned Decimal: Convert Binary to Unsigned Decimal 1111011 2 1 x 26 + 1 x 2 5 + 1 x 2 4 + 1 x 2 3 + 0 x 2 2 + 1 x 2 1 + 1 x 2 0 1 x 64 + 1 x 32 + 1 x 16 + 1 x 8 + 0 x 4 + 1 x 2 + 1 x 1 123 10 Hex to Unsigned Decimal Convert Hex to Unsigned Decimal 82D6 16 8 x 163 + 2 x 162 + 13 x 161 + 6 x 160 8 x 4096 + 2 x 256 + 13 x 16 + 6 x 1 33494 10EE 308 Spring 2011 Unsigned Decimal to Hex Convert Unsigned Decimal to Hex Division Q R Decimal Hex 721/16 45/16 2/16 45 2 0 1 13 2 1 D 2 721 10 = 2D1 16 Signed Number Representation in 2’s Complement Form: If the most significant bit (MSB) is 0 (most significant hex digit 0−7), then the number is positive. Get decimal equivalent by converting number to decimal, and use the positive (+) sign. Example for 8−bit number: 3A 16 −> + ( 3 x 161 + 10 x 160 ) 10 + ( 3 x 16 + 10 x 1 ) 10 + 58 10 If the most significant bit is 1 (most significant hex digit 8−F), then the number is negative. Get decimal equivalent by taking 2’s complement of number, converting to decimal, and using negative (−) sign. Example for 8−bit number: A316 −> - (5D) 16 - ( 5 x 161 + 13 x 160 ) 10 - ( 5 x 16 + 13 x 1 ) 10 - 93 10EE 308 Spring 2011 One’s complement table makes it simple to finding 2’s complements To take two’s complement, add one to one’s complement. Take two’s complement of D0C3: 2F3C + 1 = 2F3D One’s complement One’s complementEE 308 Spring 2011 Addition and Subtraction of Binary and Hexadecimal Numbers Setting the C (Carry), V (Overflow), N (Negative) and Z (Zero) bits How the C, V, N and Z bits of the CCR are changed N bit is set if result of operation is negative (MSB = 1) Z bit is set if result of operation is zero (All bits = 0) V bit is set if operation produced an overflow C bit is set if operation produced a carry (borrow on subtraction) Note: Not all instructions change these bits of the CCR Addition of Hexadecimal Numbers ADDITION: C bit set when result does not fit in word V bit set when P + P = N or N + N = P N bit set when MSB of result is 1 Z bit set when result is 0 7A AC +52 +72 ----- ------ CC 1E C: 0 C: 1 V: 1 V: 0 N: 1 N: 0 Z: 0 Z: 0EE 308 Spring 2011 Subtraction of Hexadecimal Numbers SUBTRACTION: C bit set on borrow (when the magnitude of the subtrahend is greater than the minuend V bit set when N - P = P or P - N = N N bit set when MSB is 1 Z bit set when result is 0 7A 2C -5C -72 ----- ------ 1E BA C: 0 C: 1 V: 0 V: 0 N: 0 N: 1 Z: 0 Z: 0EE 308 Spring 2011 Programming ModelEE 308 Spring 2011 Addressing Modes and Effective Addresses The Inherent (INH) addressing mode Instructions which work only with registers inside ALU ABA ; Add B to A (A) + (B) → A 18 06 CLRA ; Clear A 0 → A 87 The HC12 does not access memory - There is no effective address The Extended (EXT) addressing mode Instructions which give the 16−bit address to be accessed LDAA $1000 ; ($1000) → A B6 10 00 Effective Address: $1000 STAB $1003 ; (B) → $1003 7B 10 03 Effective Address: $1003 Effective address is specified by the two bytes following op codeEE 308 Spring 2011 The Direct (DIR) addressing mode Direct (DIR) Addressing Mode Instructions which give 8 LSB of address (8 MSB all 0) LDAA $20 ; ($0020) → A 96 20 Effective Address: $0020 STX $21 ; (X) → $0021:$0022 5E 21 Effective Address: $0021 8-LSB of effective address is specified by byte following op code The Immediate (IMM) addressing mode Value to be used is part of instruction LDAA #$17 ; $17 → A B6 17 Effective Address: PC + 1 ADDA #10 ; (A) + $0A → A 8B 0A Effective Address: PC + 1 Effective address is the address following the op code The Indexed (IDX, IDX1, IDX2) addressing mode Effective address is obtained from X or Y register (or SP or PC) LDAA 0,X ; Use (X) as address to get value to put in A A6 00 Effective address: contents of X INC 2,X− ; Post−decrement Indexed ; Increment the number at address (X), ; then subtract 2 from X 62 3E Effective address: contents of XEE 308 Spring 2011 INDEXED ADDRESSING MODESEE 308 Spring 2011 Relative (REL) Addressing Mode The relative addressing mode is used only in branch instructions. Branch instruction: One byte following op code specifies how far to branch Treat the offset as a signed number; add the offset to the address following the current instruction to get the address of the instruction to branch to (BRA) 20 35 PC + 2 + 0035 → PC (BRA) 20 C7 PC + 2 + FFC7 → PC PC + 2 − 0039 → PC Long branch instruction: Two bytes following op code specifies how far to branch Treat the offset as an …
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