The following 8051 assembly program is given. Answer the questions based on it.Line No. Mnemonics 1 MOV SP, #4F H 2 SET B PSW.3 3 MOV R0, #25H 4 MOV R1, #0AH 5 MOV R2, #06H 6 PUSH 8 7 PUSH 9 8 PUSH 0AH . . . V V 20 POP 8
What is stored in memory location 50 H when line 6 (PUSH 8) is executed ?
25 H
This question needs three separate facts to be combined: which register bank is active, what that makes the direct address of R0, and how PUSH works.
Step 1 — which register bank? The instruction \(\texttt{SETB PSW.3}\) sets RS0 = 1 while RS1 (PSW.4) remains 0. The bank-select bits therefore read RS1 RS0 = 01, which selects register bank 1.
| RS1 RS0 | Bank | Address range |
|---|---|---|
| 0 0 | Bank 0 | 00H – 07H |
| 0 1 | Bank 1 | 08H – 0FH |
| 1 0 | Bank 2 | 10H – 17H |
| 1 1 | Bank 3 | 18H – 1FH |
So in bank 1: R0 = address 08H, R1 = 09H, R2 = 0AH.
Step 2 — what is at address 08H? Line 3, \(\texttt{MOV R0, \#25H}\), loads the immediate value 25H into R0 — which, with bank 1 active, physically means RAM location 08H now holds 25H.
Step 3 — what does PUSH 8 push? PUSH takes a direct address as its operand, not a register name. \(\texttt{PUSH 8}\) therefore pushes the byte stored at address 08H, which is 25H. (This is why the bank matters: had bank 0 been active, R0 would be at 00H and address 08H would be R0 of bank 1 instead.)
Step 4 — where does it land? SP was 4FH, so it is pre-incremented to 50H and the byte is written there:
\(50H \leftarrow 25H\)
Why the distractors are wrong. 0AH is the value in R1 (address 09H), pushed later by line 7; 06H is in R2 (address 0AH); 4FH is the old SP value, which is never itself pushed.
Hence, memory location 50H holds 25H.
Similar Questions
A microprocessor is a semiconductor chip fabricated with entire central processing unit (CPU) on it. It is a programmable device that accepts binary data from an input device, processes the data according to the instructions stored in the memory and provides results as output. Basically microprocessor performs two functions - (a) Fetches an instruction from the memory and (b) Performs the operation specified by the instruction. There are special inputs to the microprocessor called interrupts. External devices use these interrupts to get the microprocessor attention. A micro computer can be built by using 8085 microprocessor along with many other chips such as 8155, 8255, 8279, 8253, 8257, 8259, 8251 etc. 8085 microprocessor is 8-bit microprocessor which has 8-bit data registers where as 8086 is a 16-bit microprocessor.
The following 8051 assembly program is given. Answer the questions based on it.
Line No. Mnemonics 1 MOV SP, #4F H 2 SET B PSW.3 3 MOV R0, #25H 4 MOV R1, #0AH 5 MOV R2, #06H 6 PUSH 8 7 PUSH 9 8 PUSH 0AH . . . V V 20 POP 8 $D_7$ $D_6$ $D_5$ $D_4$ $D_3$ $D_2$ $D_1$ $D_0$ In 8255 programmable peripheral interface device, if the port A and port B are to be set in a hand shake mode along with port C, what are the bits in the 8 bit control word to be set as 0 1 0.
The number system for the machine code of the microprocessor 8085 is
Which of the options in a multipurpose instruction used to implement the interrupt of 8085 and serial data input ?
Both 8155 and 8255 programmable peripheral interface ICs have the following common features :
(i) Programmable I/Os
(ii) Either port A or Port B can be set as either input or output ports.
(iii) One 14-bit down counter
(iv) AD0 – AD7 are multiplexed address/datalines.Each instruction in an assembly program has the following fields :
(i) Lable field
(ii) Operand field
(iii) Comment field
(iv) Mnemonic fieldPlease write the proper sequence of fields :
The mnemonic of 8085 processor indicate :
List – I List – II a. RLC i. Rotate Accumulator Right through carry b. RRC ii. Rotate Accumulator Left through carry c. RAR iii. Rotate Accumulator Left d. RAL iv. Rotate Accumulator Right Codes :
Match the following :
List – I (Pin terminals) List – II (Applications) a. SID, SOD i. Wait state b. READY ii. Serial data transfer c. TRAP iii. Address Latch Control d. ALE iv. Interrupt Codes :
Assertion (A) : In serial communication system, when the transmission of data goes in both ways, it is called full-duplex system. Now if two micro processors are connected in full duplex mode, the amount of data transmitted will be double to the amount of data in half-duplex mode connection.
Reason (R) : When the transmission of data goes in one way, it is called half-duplex system and when the data moves in both ways, it is called full duplex system.
Important Questions from Microprocessors
An 8086 address bus is a/an _____ -bit bus
Program counter for any counter:
In the pin out configuration of the 8085 microprocessor, the sequential input data is represented by
Which of the following functions is not performed by a microprocessor?
Match the columns.
Pin
Description
a. D 0-D 7
1. Reset Input
b. RESET
2. Data Lines
c. A 0,A 1
3. Internal Address
