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Technical articles with clear explanations and examples
Instructions to complement/set Cy flag in 8085 Microprocessor
In 8085 Instruction set, there are two instructions to control the Cy flag bit content. Thesemnemonics are STC and CMC. Both are 1-Byteinstructions. There hex codes are given in the following table – Mnemonics, OperandOpcode(in HEX)BytesSTC371CMC3F1Using STC instruction we can set the Cy flag bit to 1 irrespective of itsprevious value. And using CMC instruction we can complement the current value of the Cy fag bit andresult will update the current Cy flag bit value. Here STC stands for “SeT the Carry flag” and CMC stands for “CoMplement the Carry flag”. Note that, there isno dedicated instruction in 8085 instruction set ...
Read MoreInstructions to perform compare operation in 8085 Microprocessor
In 8085 Instruction set, we are having a set of instructions to perform compare operation where we shall compare two operands, and which will affect the status flags values depending on the result of the comparison. In this operation, 8085 imposes the restriction that one of the operands must be in the Accumulator. The other operand can be one of the following –ClassificationsExamplesThe other operand can be kept in 8-bit immediate data in the instruction.CPI 43HCPI FFHThe other 8-bit operand can be kept in a memory location and whose memory address will be pointed by HL register pair.CMP MThe other ...
Read MoreInstructions to rotate Accumulator in 8085 Microprocessor
In 8085 Instruction set, there a set of instructions which can Accumulator contents left orright. It is to be noted here that rotate operation can be performedonly on Accumulator contents. These instructions set is listed below– Mnemonics, OperandOpcode(in HEX)BytesRAL171RAR1F1RLC071RRC0F1Mnemonic RLC stands for “Rotate Left Accumulator”. It rotates the Accumulator contents to the left by 1-bit position. The following Fig. shows the operation explicitly – In this fig. it has been depicted that the mostsignificant bit of the Accumulator will come out and left rotate willcreate an empty space at the least significant bit place and thiscome out bit will be copied at ...
Read MoreConditional and Unconditional JUMP instructions in 8085 Microprocessor
In 8085 Instruction set, there are a set of jump instructions, which can transfer program control to a certain memory location. So after these branching mnemonics we shall have to mention 16-bit target address of the location. These jump instructions can be divided into two categories– Unconditional jump instructions andConditional jump instructionsUnder unconditional jump instructions there is only one mnemonic i.e. JUMP. But under conditional Jump instructions we are having 8 different mnemonics. We know that there are 5 flag bits in 8085 Flag register. They are S, Z, P, Cy, AC. Out of them only on AC flag bit, there ...
Read MoreJump if carry (JC) in 8085 Microprocessor
In 8085 Instruction set, we are having one mnemonic JC a16, which stands for “Jump if Carry” and “a16” stands for any 16-bit address. This instruction is used to jump to the address a16 as provided in the instruction. But as it is a conditional jump so it will happen if and only if the present carry flag value is 1.If carry flag value is 0, program flow continues sequentially. It is a 3-Byte instruction.Mnemonics, OperandOpcode(in HEX)BytesJC LabelDA3Let us consider one example of this instruction type JC 4000H. It is a 3-Byte instruction. The result of execution of this instruction ...
Read MoreMeasure execution time of small Python code snippets (timeit)
The Timer class and other convenience functions in timeit module of Python's standard library are designed to provide a mechanism to measure time taken by small bits of Python code to execute. The module has a command line interface and the functions can be called from within program as well.Easiest way to measure time of execution is by using following convenience functiontimeit()This function returns object of Timer class. It mainly requires two parameters.stmt − a string containing valid Python statement whose execution time is to be measured.setup − a string containing Python statement which will be executed once, primarily to ...
Read MoreUnconditional call and return instructions in 8085 Microprocessor
Sometimes in 8085assembly language coding, we require to repeat a certain program segment for multiple times. In those situations, we can define sub-routines. In those subroutines, we can enclose our repeatedly reusable Instruction set or code. And then as when required we shall call those sub-routines accordingly. Sub-routines can also be called as procedures.Whenever the instructions in a subroutine are required to be executed, we branch program control to the subroutine using th CALL instruction. CALL is a 3-Byte instruction, with 1 Byte for the opcode, and 2 Bytes for the address of the subroutine. CALL mnemonics stands for “call ...
Read MorePython Utilities for with-statement contexts (contextlib)
contextlib module of Python's standard library defines ContextManager class whose object properly manages the resources within a program. Python has with keyword that works with context managers. The file object (which is returned by the built-in open() function) supports ContextManager API. Hence we often find with keyword used while working with files.Following code block opens a file and writes some data in it. After the operation is over, the file is closed, failing which file descriptor is likely to leak leading to file corruption.f = open("file.txt", "w") f.write("hello world") f.close()However same file operation is done using file's context manager capability ...
Read MoreTop-level script environment in Python (__main__)
A module object is characterized by various attributes. Attribute names are prefixed and post-fixed by double underscore __. The most important attribute of module is __name__. When Python is running as a top level executable code, i.e. when read from standard input, a script, or from an interactive prompt the __name__ attribute is set to '__main__'.>>> __name__ '__main__'From within a script also, we find a value of __name__ attribute is set to '__main__'. Execute the following script.'module docstring' print ('name of module:', __name__)Outputname of module: __main__However, for an imported module this attribute is set to name of the Python script. ...
Read MoreBuilt-in objects in Python (builtins)
The builtins module is automatically loaded every time Python interpreter starts, either as a top level execution environment or as interactive session. The Object class, which happens to be the base class for all Python objects, is defined in this module. All built-in data type classes such as numbers, string, list etc are defined in this module. The BaseException class, as well as all built-in exceptions, are also defined in it. Further, all built-in functions are also defined in the built-ins module.Since this module is imported in the current session automatically, normally it is not imported explicitly. All the built-in ...
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