The output stream is a list of all the elements that are popped off the stack in the order that they are popped off.
a. If the input stream is ZYXWVUTSR, create a sequence of pushes and pops such that the output stream is YXVUWZSRT.
b. If the input stream is ZYXW, how many different output streams can be created.
.ORIG x3000
LEA R0, DATA
AND R1, R1, #0
ADD R1, R1, #9
LOOP1 ADD R2, R0, #0
ADD R3, R1, #0
LOOP2 JSR SUB1
ADD R4, R4, #0
BRzp LABEL
JSR SUB2
LABEL ADD R2, R2, #1
ADD R3, R3, #-1
BRp LOOP2
ADD R1, R1, #-1
BRp LOOP1
HALT
DATA .BLKW #10
SUB1 LDR R5, R2, #0
NOT R5, R5
ADD R5, R5, #1
LDR R6, R2, #1
ADD R4, R5, R6
RET
SUB2 LDR R4, R2, #0
LDR R5, R2, #1
STR R4, R2, #1
STR R5, R2, #0
RET
.END
- The program below counts the number of zeros in a 16-bit word. Fill in the missing blanks below to make it work.
.ORIG x3000 AND R0, R0, #0 LD R1, SIXTEEN LD R2, WORD A BRn B ________________ B ________________ BRz C ________________ BR A C ST R0, RESULT HALT SIXTEEN .FILL #16 WORD .BLKW #1 RESULT .BLKW #1 .END - After you have the correct answer above, what one instruction can you change (without adding any instructions)
that will make the program count the number of ones instead?
Note: All blanks must be filled for the program to operate correctly.
MUL _______________
ST R0, SAVER0
ST R1, SAVER1
ST R2, SAVER2
ST R5, SAVER5
AND R2, R2, #0
JSR POP
ADD R1, R0, #0
JSR POP
ADD R1, R1, #0
_______________
AGAIN ADD R2, R2, R0
_______________
BRp AGAIN
DONE ADD R0, R2, #0
JSR PUSH
_______________
LD R0, SAVER0
LD R1, SAVER1
LD R2, SAVER2
LD R5, SAVER5
RET
Note: Assume that the value stored at NUM will be between 0 an 81.
.ORIG x3000
AND R2, R2, #0
LD R3, NUM
BRz OUTPUT
NOT R3, R3
ADD R3, R3, #1
OUTLOOP ADD R2, R2, #1
_______________
AND R1, R1, #0
INLOOP ADD R1, R1, R2
ADD R0, R0, #-1
BRp INLOOP
_______________
BRn OUTLOOP
OUTPUT LD R0, ZERO
_______________
TRAP x21
HALT
NUM .BLKW 1
ZERO .FILL x30
.END
The initial values of some of the processor registers and the I/O registers, and some memory locations are as follows:
| R0 = x0000 PC = x3000 | KBSR = x8000 KBDR = x0061 DSR = x8000 DDR = x0031 | M[x3009] = xFE00 M[x300A] = xFE02 M[x300B] = xFE04 M[x300C] = xFE06 |
During the entire instruction cycle, memory is accessed between one and three times (why?). The following table lists two consecutive instructions to be executed on the LC-3. Complete the table with the values that each signal or register takes right after each of the memory accesses performed by the instruction. If an instruction does not require three memory accesses, draw a line accross the unused accesses. To help you get started, we have filled some of the values for you.
| PC | Instruction | Access | MAR | A | B | C | D | E[15:0] | F[1] | F[0] | MDR |
| x3000 | LD R0, x9 | 1 | x3000 | x2009 | |||||||
| 2 | |||||||||||
| 3 | |||||||||||
| x3001 | LDR R0, R0, #0 | 1 | |||||||||
| 2 | |||||||||||
| 3 |
A programmer wrote this program to do something useful. He, however, forgot to comment his code, and now can't remember what the program is supposed to do. Your job is to save him the trouble and figure it out for him. In 20 words or fewer tell us what valuable information the program below provides about the value stored in memory location INPUT. Assume that there is a non-zero value at location INPUT before the program is executed.
HINT: When testing different values of INPUT pay attention to their bit patterns. How does the bit pattern correspond to the RESULT?
.ORIG x3000
LD R0, INPUT
AND R3, R3, #0
LEA R6, MASKS
LD R1, COUNT
LOOP LDR R2, R6, #0
ADD R3, R3, R3
AND R5, R0, R2
BRz SKIP
ADD R3, R3, #1
ADD R0, R5, #0
SKIP ADD R6, R6, #1
ADD R1, R1, #-1
BRp LOOP
ST R3, RESULT
HALT
COUNT .FILL #4
MASKS .FILL 0xFF00
.FILL 0xF0F0
.FILL 0xCCCC
.FILL 0xAAAA
INPUT .BLKW 1
RESULT .BLKW 1
.END