Basic Instruction Set - Microprocessor Based Systems - Lecture Slides, Slides of Microprocessor and Interfacing

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Basic Instruction Set

Lecture Overview

• The M68HC11 Basic Instruction Set
  • How to partition the instruction set to learn it
  • What are those partitions
  • The 68HC11 data movement instructions
• Material from Chapter 2 and 3 plus a 68HC reference manual. Instruction set details are in Appendix A of the text.

Basic guide (cont.)

• Instruction classes continued
  • Condition Code Register
  • Branch – what conditional branches are supported
  • Jump – direct? How different from Branch?
  • Subroutine Calls and Return – calls that save register and data and calls that don’t.
  • Stack Pointer
  • Index Register and Indexed access to data
  • Interrupts and Interrupt Handling
  • Any miscellaneous instructions

Data Movement

• These instructions allow for the transfer of data from one location to another.
• In a RISC (Reduced Instruction Set Computer) these transfers are the only data movement instructions. Operational instructions are typically register to register with both operands being in register to start.
• In a CISC (Complex Instruction Set Computer) there are complex instruction that not only perform the operation on data but also result in complex data movement and/or storage.

CLR

• Operation: ACCX  0 or M  0
• Description: The contents of the accumulator or the memory location are set to 0s.
• CC effects: N, V, C are cleared, Z is set
• Forms: CLRA CLRB CLR

Load data

• Operation: place the operand data into accumulator A, B, or D.
• Description: Load the accumulator
• CC effects: V cleared, N and Z set or cleared depending on value of data.
• Forms: LDAA LDAB LDD

Store data

• Operation: Store the accumulator at the effective address.
• Forms: STAA
• STAB
• STD

The Stack

• The stack is an area of RAM used for temporary storage, typically for subroutine calls and then the subsequent return. It is also used when servicing and interrupt.
• One of the Programmers Model registers is the stack pointer register. This is a 16-bit register that points to the next free location on the stack. The stack grows down in memory.

Push and Pop

• Two common operations on stacks are to add data, a Push, and the retrieval of data, a Pop.
• For the 68HC
  • A PUSH – Simply store the data at the address pointed to by the stack pointer. After storing the data, decrement the stack pointer.
  • A POP – Increment the stack pointer. Use the data that the stack pointer now points to. Location is now considered free.

Push and Pull

• Operation: A/B  Mem(SP) Pull
• Mem(SP)  A/B Push
• Description: Transfers the contents of the Accumulator to or from the top of the stack.
• CC effects: none
• Forms: this is an inherent instruction
  • PSHA PSHB PULA PULB

Transfer register

• Operation: Transfers allowed are
• from A to B or CCR
• from B to A
• from CCR to A
• Description: Transfers the contents of one register to another.
• CC effects: A to B and B to A  N V Z
• Forms: only inherent

Exchange registers

• Operation: D  X concurrent with X  D
• D  Y concurrent with Y D
• Description: Exchange the contents of the D accumulator with the X or Y index register
• CC effects: None
• Forms: Inherent form instruction

Assignment

• Read Chapter 3 through section 3.
• Problems