6 (2 points) Is the pin IRQ active high or active low? 7. (5 points) What is the

Question

6 (2 points) Is the pin IRQ active high or active low? 7. (5 points) What is the react vertor for the 68HC117 8. (5 points) Describe the FETCH-EXECUTE cycle 9. (5 points) Name 3 CCR flags 10. (10 points) Name 10 different 68HC11 instructions. Using different accumulators does not count as different instructions. 11. (10 points) Draw the timing disgram for the basic write cycle to a DRAM 12. For a 256x8 SRAM find (a) (2 points) the required number of data lines to support the chip (b) (2 points) the required number of address lines to support the chip (c) (2 points) the capacity in bytes 13. (5 points) What is the pin on the 68HC11 that we can use to indicate whether we are in a read or write cycle? In your answer state how we tell which state is which

Explanation / Answer

6) The interrupt pin is active LOW

7) After reset, the CPU fetches the reset vector from locations $FFFE and $FFFF ( $BFFE and $BFFF in the special test or bootstrap mode) during the first three cycles and begins instruction execution

8) The following is the flow of fetch and execute

Program Counter (PC) holds address of next instruction to fetch

• Processor fetches instruction from memory location pointed to by PC

• Increment PC —Unless told otherwise

• Instruction loaded into Instruction Register (IR)

• Processor interprets instruction and performs required actions Execute Cycle

• Processor-memory —data transfer between CPU and main memory

• Processor I/O —Data transfer between CPU and I/O module

• Data processing —Some arithmetic or logical operation on data

• Control —Alteration of sequence of operations —e.g. jump

9)

CCR Condition Code Register

BEQ: Branch if Equal to Zero

Branch is made if Z flag is 1 (indicating a zero result).

BNE: Branch if Not Equal to zero:

Branch is made if Z flag is 0 (indicating a non-zero result).

BCC: Branch if Carry is Clear

Branch is made if C flag is 0, indicating that a carry did not result from the last operation.

BCS: Branch if Carry is Set

Branch is made if C flag is 1, indicating carry occurred.

BLO: Branch if Lower

Branch is made if result of subtraction was less than zero. This instruction works correctly when using unsigned data.

BGE: Branch if Greater Than or Equal

Branch is made if result of subtraction is greater than or equal to zero. This instruction works correctly only when using unsigned data.

10)

Clear Memory Byte CLR

Add Accumulators ABA

Add with Carry to A ADCA

Compare A to Memory CMPA

Decrement Accumulator A DECA

Increment Memory Byte INC

Increment Accumulator A INCA

Multiply (A × B D) MUL

AND A with Memory ANDA

One’s Complement A COMA

Branch if Bit(s) Clear BRCLR

Branch if Bit(s) Set BRSET

Arithmetic Shift Left Memory ASL

Arithmetic Shift Left A ASLA

Clear Carry Bit CLC

Clear Interrupt Mask Bit CLI

Clear Overflow Bit CLV

Set Carry Bit SEC

Set Interrupt Mask Bit SEI

Set Overflow Bit SEV

Transfer A to CCR TAP

Transfer CCR to A TPA X

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