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.
(i), (ii) and (iv)
Feature (iii) is the clearest discriminator: the 14-bit down counter is a distinguishing feature of the 8155 alone, so any option containing it must be rejected. That eliminates options 1, 3 and 4 at a stroke and leaves option 2.
| Feature | 8155 | 8255 |
|---|---|---|
| (i) Programmable I/O ports | ✓ | ✓ |
| (ii) Port A / Port B settable as input or output | ✓ | ✓ |
| (iii) 14-bit down counter | ✓ | ✗ |
| (iv) Multiplexed AD0–AD7 | ✓ | Strictly ✗ |
| On-chip RAM | 256 bytes | None |
What the two devices actually are. The 8255 is a pure peripheral interface: three 8-bit ports (A, B and C) and a control register, nothing more, and it needs an external latch to demultiplex the 8085's bus. The 8155 is a combination chip designed to make a minimum-component system possible — 256 bytes of static RAM, two 8-bit ports plus a 6-bit port, a 14-bit timer/counter, and a built-in address latch so it connects directly to the multiplexed AD bus. A single 8085, an 8155 and an EPROM make a complete microcomputer.
Why the answer is flagged. Feature (iv) is not strictly common either: the 8255 has plain data lines D0–D7 and no internal latch, so demultiplexing must be done outside with an 8212 or 74LS373. On a strict reading only (i) and (ii) are shared, and no option offers that pair alone. Option 2 is the intended answer because it is the only one free of the counter, which is the unambiguous 8155-only feature; feature (iv) is evidently included in the loose sense that both chips sit on the same 8085 bus.
The 14-bit counter itself is worth a note, since the odd width is often asked: two bytes are loaded, but the top two bits of the high byte select the output mode — single pulse, continuous square wave, and so on — leaving fourteen bits for the count.
Hence, the answer as printed is (i), (ii) and (iv).
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 ?
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.
The assembler directive used to give name to some value or symbol for 8086 ASM-86 is
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
