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What is read modify write technique?- Read modify write is a technique used to access the ports.
- Here in a single instruction all the three actions are combined.
- Here initially the data is read from the port then modified .
- At last the value is written back on the port.
- This feature saves many lines of code and makes the process easier.
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In which addressing mode is the DPTR register used?- Data pointer register is used in the indexed addressing mode.
- It is used in accessing data from tne look-up table entries stored in ROM.
- SYNTAX: MOVC A, @A+DPTR
- Here c means the code (shows data elements are stored in code space of ROM).
- The contents of A are added to 16 bit DPTR to form the 16 bit address of the needed data.
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Which registers are used for register indirect addressing mode if data is on-chip?- R0 and R1 are the only registers used for register indirect addressing mode.
- These registers are 8 bit wide.
- Their use is limited to accessing only internal RAM.
- When these registers hold addresses of RAM, they must be preceded by a @ sign.
- In absence of this sign it will use the contents of register than the contents of memory location pointed by the same register.
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Of the 128-byte internal RAM how many bytes are bit addressable?- Only 16 bytes of the 128 bytes of RAM are bit addressable.
- The bit addressable RAM locations are 20H to 2FH.
- They are addressed as 0 to 127 (decimal) or 00 to 7F.
- Also the internal RAM locations 20 to 2FH are both byte and bit addressable.
- These 16 bytes can be by single bit instructions using only direct addressing mode.
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Explain parallel address space.- The two physically separate memories using the same addresses form the parallel address space.
- Here the two memories are accessed using different access modes.
- This parallel addressing is generally used in 8052(enhanced version of 8051) having extra 128 bytes of RAM with addresses 80 to FFH and memory is called as upper memory.
- This distinguishes it from lower 128 bytes 00to 7FH.
- To access lower bytes direct addressing mode is used and for higher bytes indirect addressing mode is used.
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Which port in 8051 performs a dual role?- The port 3 can be used as simple input /output port or provides signals like interrupts.
- P3.0 and p3.1 are used for serial communication.
- P3.2 and P3.3 are used as external interrupts.
- P3.4 and P3.5 are used for timers.
- P3.6 and P3.7 are used as read write signals of external memory.
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Explain high-end embedded processor.- The microcontroller & processor can be interchangeably used here.
- It forms a general purpose processor .
- High-end stands for system of greatest power.
- Here when a microcontroller cannot do a specific task the processor does the same with higher power
- Example: ADM 64
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Which 8051 version is using UV-EPROM?- Ultraviolet EPROM is used in the version 8751.
- Here it becomes easier to erase the data using uv rays.
- It takes around 20 minutes to erase the data.
- To overcome this short coming flash ROM versions of 8751 available.
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Which 8051 version uses Flash ROM?- Atmel Corporation is manufacturing flash ROM
- At 89C51 chip of atmel is using flash ROM.
- Here no Rom eraser is needed.
- Erasing process is done by the PROM burner itself.
- To avoid use of PROM burner the 8052 version support in-system programming.
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In which registers the immediate values cannot be directly loaded?- The general purpose registers named A,B, R0-R7 can not accept the immediate data.
- To indicate immediate value pound sign is used before it.
- These register accept 8 bit data preceding a pound sign.
- There are registers present in 8051 used to store data temporarily.
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Explain the difference between statements.
MOV A, #17H -a
MOV A, 17H -b- Statement a indicates immediate data is copied into the register A.
- # in statement a indicates 17 is an immediate data which is moved to the destination.
- Here one copies the immediate data and other copies the data present at the specified address.
- In statement b the value present in 17H memory location is copied into A register.
- Absence of pound sign does not cause any error but required operation fails.
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Which register is considered as the destination register for any arithmetic operation.The ‘A’ register called the accumulator is used as the destination register. Example:ADD R2, # 12H This is invalid as 12 is to be added to value present in R2 and data is also stored in R2. ADD A,# 12H This is valid as 12 is to be added to the value present in accumulator. Foregoing discussion explains why register A is used as accumulator.
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Explain LCALL.- It is called long call and is a 3 byte instruction.
- Here 1st byte is used for opcode &2nd & 3rd bytes are used for address of target subroutine.
- Call subroutine can be used anywhere within 64 K- byte address space.
- Processor automatically saves on stack the address of instruction immediately below LCALL.
- After execution instruction return (RET) transfers control back to next instruction.
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How much time is required by an instruction for execution in 8051?- Time required depends on the number of clock cycles used to execute instruction.
- These clock cycle are called machine cycle.
- Length of machine cycle of an instruction depends on frequency of crystal oscillator of controller.
- Also one machine cycle lasts 12 oscillator period so machine cycle is 1 \12 of crystal frequency.
- Crystal frequency 8051 = 11.0592MHz
- Machine cycle = 11.0592MHz\12 = 921.6KHz = 1.085micro second.
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