ECE 265 – LECTURE 7
The M68HC11 Basic Instruction Set
Logical, Shift and Rotate, Data Testing
4/15/2020
ECE265 1

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Lecture Overview
 The M68HC11 Basic Instruction Set
 The Logical instructions to perform Boolean operations
 The Data Testing
 The Shift and Rotate instructions
 REF: Chapter 3 and the appendix that details the instructions.

Joanne E. DeGroat, OSU ECE265 4/15/2020

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The Logical Instructions
 Instructions to perform Boolean operations on data

Instructions for AND NOT and OR operation
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Joanne E. DeGroat, OSU ECE265 4/15/2020

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AND operation
 Description: AND the A (or B) accumulator with the operand of the instruction
 CC effects: N Z set per result

Forms: ANDA (opr) ANDB(opr)
 And can be immediate mode or a memory location
 ANDA #$FF What does this do?
 ANDB #$00 What does this do?
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Joanne E. DeGroat, OSU ECE265 4/15/2020

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AND operation and masking
 Masking is keeping only those bits you are interested in. The reaming bits are “masked” out.
 Example

ANDA #$0F Keep the lower 4 bits of accum A
 If the A accumulator contains a value of $34
 Then this operation is A 0011 0100


AND-ed with 0000 1111 giving 0000 0100
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Joanne E. DeGroat, OSU ECE265 4/15/2020

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OR operation
 Description: OR the A (or B) accumulator with the operand of the instruction
 CC effects: N Z set per result

Forms: ORA (opr) ORB(opr)
 And can be immediate mode or a memory location
 ORAA #$FF What does this do?
 ORAB #$00 What does this do?
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Joanne E. DeGroat, OSU ECE265 4/15/2020

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Exclusive OR operation
 Description: Exclusive OR the A (or B) accumulator with the operand of the instruction
 CC effects: N Z set per result

Forms: EORA (opr) EORB(opr)
 And can be immediate mode or a memory location
 EORA #$FF What does this do?
 EORB #$00 What does this do?
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Joanne E. DeGroat, OSU ECE265 4/15/2020

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The NOT or invert operation
 Description: Can complement a complete byte in an accumulator or memory. This is a bitwise complement.
 CC effect: N V set per data, V cleared, C set
 Forms: COMA COMB COM (opr)
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Joanne E. DeGroat, OSU ECE265 4/15/2020

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Examples
 Example instructions
Accum A has val $1C
Memory $D330 val $2F
 (a) ANDA $D330

(b) EORA $D330
 (c) ORAA $D330
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Joanne E. DeGroat, OSU ECE265 4/15/2020

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Data Testing Instructions
 Will cover the Bit Test and Setting and Clearing of bits.
 The branch will be covered with branches.

Joanne E. DeGroat, OSU ECE265 4/15/2020

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Bit test
 Description: Compare the operand with the accumulator contents and set the CC bits.
Performs a bitwise logical AND.
 CC effects: N Z eval V cleared
 Forms: BITA (opr) BITB (opr)
 If operand is equal to accumulator Z is set
 See Appendix A of text for a complete description

Joanne E. DeGroat, OSU ECE265 4/15/2020

Clear and set bits in memory
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
Description: Set or Clear bits in memory according to a mask given in the instruciton.
 CC effects: N Z V cleared

Forms: BSET (opr) (mask) BCLR (opr) (mask)

Example BSET $0035 $09
 Performs a logical OR of the contents of location $35
 With $09 and puts the result back in the location.
 This example will set bits 0 and 3 of the data byte.

Joanne E. DeGroat, OSU ECE265 4/15/2020

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Shift and Rotate Instructions
 The instructions perform arithmetic and logical shifts and also rotate the data.

Joanne E. DeGroat, OSU ECE265 4/15/2020

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The effect of shift and rotates
 What do the instructions do?

Joanne E. DeGroat, OSU ECE265 4/15/2020

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What is the real effect of
 Arithmetic shifts?
 Do arithmetic shifts have the effect of multiplicaiton?

Unique aspects of logical shifts
 Can also do double shifts
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Joanne E. DeGroat, OSU ECE265 4/15/2020

The instructions
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
Arithmetic Shifts
 ASL (opr) ASLA ASLB ASLD
 ASR (opr) ASRA ASRB

Logical Shifts
 LSL (opr) LSLA LSLB LSLD
 LSR (opr) LSRA LSRB LSRD
 Rotates
 ROL (opr) ROR (opr)
 ROLA ROLB RORA RORB
 There is no rotate of D
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Joanne E. DeGroat, OSU ECE265 4/15/2020

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Example of use
 Interesting data manipulation
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Joanne E. DeGroat, OSU ECE265 4/15/2020

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Example of use
 Exchange the upper and lower nibbles of a byte in memory.
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Joanne E. DeGroat, OSU ECE265 4/15/2020

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Lecture summary
 Have covered
 The Logical instructions to perform Boolean operations
 The Data Testing
 The Shift and Rotate instructions

Joanne E. DeGroat, OSU ECE265 4/15/2020

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Assignment
 Problems Chapter 3 page 87
 Problem 19
 Problem 21
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Joanne E. DeGroat, OSU ECE265 4/15/2020