ME 4447/6405 Microprocessor Control of Manufacturing Systems and Introduction to Mechatronics Instructor: Professor Charles Ume Lecture #10

Relative Addressing

Relative Addressing Relative addressing is used for branch instructions only. Three types of branch instructions: Short Branches – offset signed 8-bit number (-128 to 127) Long Branches – offset signed 16-bit number (-32,768 to 32,767) Bit Condition Branches – offset signed 8-bit number (-128 to 127) Short Branch instructions are 2 bytes in length. First byte contains opcode Second byte contains address offset BEQ Loop 27 offset (I byte)

Relative Addressing Long branch instructions are 4 bytes in length First two bytes contain opcode and postbyte Second byte contains 16-bit signed address offset LBEQ Loop 18 27 MSB LSB  offset value Bit condition branch instructions are 4 to 6 bytes in length depending on addressing mode BRSET $0800 #$05 Loop 1E 08 00 05 1 byte offset value Offset is calculated by subtracting contents of Program Counter from destination address. (Note: The Program Counter contains the memory location of the next instruction) If branch condition is true, then add offset to program counter

Example 1 Example Program assembled except for the relative addresses (offsets) ORG $1000 Address Opcode Postbyte Operand ABA $1000 18 06 : : BACK LDAA #$30 $106A 86 30 NEGA $106C 40 ADDA $1A00 $106D BB 1A00 BEQ FRONT $1070 27 ADDA $31 $1072 9B 31 BNE BACK $1074 26 FRONT NOP $1080 A7 SWI 3F END Offset ? Offset ?

Example 1 First calculate address offset for forward branch ORG $1000 Address Opcode Postbyte Operand ABA $1000 18 06 : : BACK LDAA #$30 $106A 86 30 NEGA $106C 40 ADDA $1A00 $106D BB 1A00 BEQ FRONT $1070 27 ADDA $31 $1072 9B 31 BNE BACK $1074 26 FRONT NOP $1080 A7 SWI 3F END Offset ? Offset ?

Example 1 Branching Forward Offset is positive if branching forward

Example 1 Address of BEQ instruction and Address of where to jump to (NOP) ORG $1000 Address Opcode Postbyte Operand ABA $1000 18 06 : : BACK LDAA #$30 $106A 86 30 NEGA $106C 40 ADDA $1A00 $106D BB 1A00 BEQ FRONT 27 ADDA $31 $1072 9B 31 BNE BACK $1074 26 FRONT NOP A7 SWI 3F END $1070 Offset ? Offset ? $1080

Step2: Subtract result from destination address $1080-$1072 = $0E Example 1 Branching Forward Continued In Hexadecimal Step1: Add $02 to starting address $1070+$02 = $1072 to determine contents of Program Counter Step2: Subtract result from destination address $1080-$1072 = $0E Address Offset is : $0E $1070 0001 0000 0111 0000 + $02 0000 0000 0000 0010 $1072 0001 0000 0111 0010 1’s COMP 1110 1111 1000 1101 2’s COMP 1110 1111 1000 1110 +$1080 0001 0000 1000 0000 0000 0000 0000 1110 = $0E

Example 1 Calculate address offset for backward branch ORG $1000 Address Opcode Postbyte Operand ABA $1000 18 06 : : BACK LDAA #$30 $106A 86 30 NEGA $106C 40 ADDA $1A00 $106D BB 1A00 BEQ FRONT $1070 27 0E ADDA $31 $1072 9B 31 BNE BACK $1074 26 FRONT NOP $1080 A7 SWI 3F END Offset ?

Example 1 Branching Backward Offset negative if branching backward

Example 1 Address of BNE instruction and Address of where to jump to (LDAA) ORG $1000 Address Opcode Postbyte Operand ABA $1000 18 06 : : BACK LDAA #$30 86 30 NEGA $106C 40 ADDA $1A00 $106D BB 1A00 BEQ FRONT $1070 27 ADDA $31 $1072 9B 31 BNE BACK 26 FRONT NOP $1080 A7 SWI 3F END $106A $1074 Offset ?

Example 1 Branching Forward Continued In Hexadecimal Step1: Add $02 to starting address $1074+$02 = $1076 to determine contents of Program Counter Step2: Subtract result from destination address $106A-$1076 But result will be negative so: Step 3: Switch order and subtract $1076-$106A = $0C Step 4: Take 1’s complement $0C -> $F3 Step5: Take 2’s complement $F3 + $01 = $F4 Address offset will be: $F4

Example 1 Branching Forward Continued Note: In Binary $1074 0001 0000 0111 0100 + $02 0000 0000 0000 0010 $1076 0001 0000 0111 0110 1’s COMP 1110 1111 1000 1001 2’s COMP 1110 1111 1000 1010 +$106A 0001 0000 0110 1010 1111 1111 1111 0100 = $F4

Example 1 Example Program assembled completely ORG $1000 Address Opcode Postbyte Operand ABA $1000 18 06 : : BACK LDAA #$30 $106A 86 30 NEGA $106C 40 ADDA $1A00 $106D BB 1A00 BEQ FRONT $1070 27 0E ADDA $31 $1072 9B 31 BNE BACK $1074 26 F4 FRONT NOP $1080 A7 SWI 3F END

Address Opcode Postbyte Operand Long Branch Instructions Long branch instructions are equivalent to short branch instructions, except offset is signed 16-bit number [-32,767 to 32,768] Example: Assume distance from branch instruction to destination is greater than 127 memory locations. Must use long branch instructions: Short Branch: BNE FRONT $1074 26 0A : : FRONT NOP $1080 A7 Long Branch: LBNE FRONT $1074 18 26 040A FRONT NOP $1480 A7 Address Opcode Postbyte Operand

Example Branch Instructions Branch if bit(s) clear (BRCLR) Example: Branch to DOG when bit 0 and bit 2 are clear in data contained at address $19 BRCLR $19 #$05 DOG Assume $19 contains #$63 #$63 = 0110 0011 #$05 = 0000 0101 (MASK) will not branch to DOG Assume $19 contains #$62 #$62 = 0110 0010 #$05 = 0000 0101 (MASK) will branch to DOG (Note: BRCLR may be used in extended addressing mode.) Can also be written as: LDY #$0019 BRCLR $00,Y #$05 DOG

Example Branch Instructions Branch if bit(s) set (BRSET) Example: Branch to DOG when bit 0 and bit 2 are set in data contained at address $20 BRSET $20 #$05 DOG Assume $20 contains #$63 #$63 = 0110 0011 #$05 = 0000 0101 (MASK) *will not branch to DOG Assume $20 contains #$65 #$65 = 0110 0101 #$05 = 0000 0101 (MASK) *will branch to DOG Can also be written as: LDX #$0020 BRSET $00,X #$05 DOG

Branch Instructions from Programming Reference Guide

Branch Instructions from Programming Reference Guide (continued) (Note: BRCLR and BRSET boxed in Red)

Special Instructions Bit Clear Example: BCLR $34 #$04 Assume $34 contains #$44 #$44 = 0100 0100 #$04 = 0000 0100 Result: $34 will now contain 0100 0000 Alternative: If index register X contains #$0034, we can use the following instruction to perform the same operation as above. BCLR $00,X #$04

Special Instructions Cont’d Bit Set Example: BSET $00,X #$01 Assume the content of index register X is #$0045 and assume that $45 contains #$60. #$60 = 0110 0000 #$01 = 0000 0001 Result: $45 now contains 0110 0001 Alternative: We can use the following instruction to perform the same operation as above. BSET $45 #$01

Special Instructions Cont’d BITA This instruction is similar to ANDA except that the result of this operation is not stored in accumulator A. Example: BITA #$7C BNE LOOP Assume accumulator A contains #%11110001 #$7C = #%01111100 Result: The operation produces the result #%01110000 but this is not stored anywhere. The following instruction will branch to LOOP because the result of the preceding operation was not equal to zero.

Homework Set #3 Solution 1. Write a subroutine to save the first 5 odd (8-bit) numbers pointed to by the x-register (passed in) onto the stack. Note: For subroutine to execute in main program, a BSR or JSR command must be used in main program. 2. Write a program to output a square wave thru port S pin The output can be observed on the scope, and the period T of the wave should be measured. More than one period wave should be generated. The machine cycle time of the MC9S12C32 should be estimated. Draw the square wave.

QUESTIONS???