ECE 252 Week 8

To find the first memory address for PC-offset addressing assigned by the compiler, take:

0x0200 + Number of instructions, including BR START

Nibble

4 bits

LOAD instruction LC-3

A load instruction copies a value from a memory location to a register. EX: LD R0, NUM -Load whatever is in memory location named NUM into R0

Indirect addressing concept

A location in memory holds a value which is the final memory address.

LDR and STR use what type of addressing

Base-offset addressing

Effective Address for PC-relative Addressing mode

Effective Address= PC+ + PCoffset

PC-relative addressing mode

Instead of encoding the actual address, encode how far away it is from where the already-incremented PC is pointing. It is used for accessing memory locations "near" the current PC value, since the 9-bit offset is limited in range.

LC-3 LDI instruction

LDI R4, ADDR_R **Read from the location labeled ADDR_R to get the effective address for a load that copies from memory to register R4.

LC-3 base offset Load

LDR DR, BaseR, offset6

LC-3 load effective address

LEA, R1, ARRAYLABEL -Copy the address of the ARRAY label into register R1 so that we can use it as a base register for LDR/STR

Assembler directive to create a label

NAMEOFLABEL .FILL x1234

LD and ST use what type of addressing

PC relative

LC-3 STI instruction

STI R4, ADDR_W **Read from the location labeled ADDR_W to get the effective address for a store that copies from register R4 to memory.

LC-3 base offset store

STR DR, BaseR, offset6

Labels in Assembly language

Somewhat like a variable in a HLL. The assembler converts the labels to addresses.

Base-offset Addressing

The value of the base register is added to the signed offset to get the effective address

STORE instruction LC-3

a store instruction copies a value from a register to a memory location EX: ST R6, NUM -Copy whatever is in register R6 to the memory location named NUM