Chapter 1: Data & Memory Flashcards
Each binary digit is a
bit
A byte is
8 bits
A nibble is
4 bits
The PIC microcontroller instruction set information:
The PIC microcontroller that you will be using has 14-bit instruction words and 8-bit data words
The sequence of instructions executed by a chip is commonly known as a
program
Where is the program stored?
non-volitile memory
Data memory is split up into different areas such as
the stack, heap and general data area (GDA)
How is memory accessed by the instruction set?
Each piece of memory has a unique address that an instruction can use to access that byte of data
What is a microprocessors memory map?
- The memory map of a microprocessor gives you the addresses of different types of memory.
- Addresses are usually given in hexadecimal.
- Even inputs and outputs are shown as it is common to ‘memory map’ them for simplicity, i.e. give them an address to make them look like just another piece of memory.
What determines the speed at which a processor can execute the instruction set?
The speed at which the processor can execute a programme is determined mainly by the speed at which it can access data.
Different types of memory storage can be accessed at different speeds and can vary greatly in cost. Typically the faster memory is also the most costly.
Fast Memory speed details:
- Registers are the fastest type of memory and can be directly addressed by processor machine code instructions.
- The cache is the next fastest and is co-located with the processor and provides fast memory access to locations likely to be needed often.
Issues with main memory speed access?
Main memory requires a bus transaction to access. Typical access time is a few cycles. Storage systems (disk, flash etc.) require multiple bus accesses to configure the relevant I/O controller. Typical access time is hundreds of cycles.
Explain what a program counter does?
A special register called the programme counter marks the address of the current instruction being carried out and increments by one with each instruction.
You can change the linear flow of a programme by adjusting the programme counter.
What is needed for the programmers model?
- Description of all instructions: The Instruction Set
- Memory map
- Details of the registers
- Vector information, i.e. places to look for programs and when to execute them (e.g. on power-up/reset, interrupt vector)
How is timing controlled on a microprocessor?
The speed at which a microprocessor executes instructions is determined by the clock
Diagram for Von Neumann architecture?
The key aspects of Von Neumann architecture?
The key aspect is that a single block of memory contains both the programme and the data.
This memory is connected to the CPU by a single bus.
A bus is a digital data highway consisting of a number of parallel wires.
Advantages of Von Neumann architecture?
The advantages of this architecture are that there is a single address space, i.e. a single memory map describes all instruction and data areas, and that the system can compile its own software.
Disadvantages of Von Neumann architecture?
The disadvantage is that since there is a single bus, programme instructions and data have to take their turn on it, which leads to congestion.
Since the processor typically operates much faster than it takes to access data from memory, the bus becomes the ‘bottleneck’ that limits the overall speed of the processor.
Harvard architecture diagram?
The key aspects of Harvard architecture?
It has separate memory blocks for the programme instructions and the data with separate data and address buses.
Advantages of Harvard architecture?
- Since there are separate buses, instructions and data may be accessed at the same time. Therefore Harvard architecture processors can be faster, at the expense of being more complicated.
- data and address buses can be different sizes, i.e. carry a different number of bits; instructions do not need to have the same number of bits as the data word.
The disadvantage of Harvard architecture?
A disadvantage is that these processors are not capable of downloading new programmes to itself. An example of the Harvard architecture is the PIC microcontroller.
