SCM single chip microcomputer 1st note, communication

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The principal of Microcomputor: hardware communication

1.Serial VS Parallel communications
  Most of electronic equipment are based on serial technology, and here we need to explain why it’s better than parallel communication, that will help us in the understanding of data communication of these hardware.
  Serial com will transport the data Byte by Byte, seemingly it has a lower efficiency than parallel com, while is that true? If we compare both of them under the real physical world, we’ll find that the noise is a headache thing. Once we use the parallel com, it will generate more than one line to send the data, but it’s impossible to make all the physical line to be the same, which mean they will have different reaction to the same noise, especially when the data linked to some analog signal, they are fractured as differential signal, for these signals, noise will make a great influence. For the serial com, most of the noise can be offset to the simple line, but to the parallel com, the difference to the different line is impossible
2.CPU transmit data with peripherals equipment
2.1 Querying the transmission mode
  Whether the SCM(single chip microcomputer) is running or not, most of the time it’s in the free time, so the main chip won’t always work or waiting for signal, instead, it will check if there is any new instruct received from the peripheral equipment, the concrete method is the query, timely communicate with other part is a useful function to keep the SCM from sleeping.
2.2 Interrupt transmission mode
  In contrast to the querying mode, the SCM will be working in the interrupt mode, after getting some valid instruct and execute it. the CSM will not execute other instruct until it finish the task at present.
2.3 DMA(Direct Memory access)
  That’s a another access to have have communication with other equipment, most of the time, SCM will cost much of it’s internal storage to keep data and move it inside of the SCM, while if we need only disposal the data only in the SCM itself. The programmer can choose to open the DMA to cut down the storage cost, then it will improve the efficiency, too.
3.Assemble language
  Of course the SCM need to learn assemble language, actually the assemble language can be the base of flash bonding, so I will start a column for it, now we will just talk about some basic knowledge like: simple phrase(MOV), a line of code can be only correspond to a piece of instruct in computer. That’s totally different from C or python since they are senior language, their single function will reflect to many piece of instruct for assemble language. And for different electrical equipment, they have different phrase about assemble language. But however, it’s a must for we to learn if we want to know flash bonding.
4. Time module in SCM
   Time module is totally different from FPGA, there is a exist time part(Unified Clock System,UCS) for you to call for, and you can’t use the crystal oscillator. Never use digital time series in SCM, actually UCS simplified the difficulty of SCM time module. Every digital equipment is required a public clock standard, otherwise the system will work in different time interval. For example, the main chip work in a nanosecond as a unit while some function chip work in a millisecond, then the two is not able to communicate with each other. However, although the inventor had simplify the system, it is hard to use the UCS since it is complicated. here I need to get clear about some terms in the SCM which is related to the MSP430×5×× series SCM:

UCS,Unified Clock System

The UCS module supports low system cost and ultralow power consumption. Using three internal clock signals, the user can select the best balance of performance and low power consumption. UCS module includes five sources: XT1CLK VLOCLK REFOCLK DCOCLK XT2CLK;
with the five sources, the SCM formed 3 clock for system:
ACLK: Auxiliary Clock
MCLK: Master Clock
SMCLK: Subsystem Master Clock
The three are available divided by 1, 2, 4, 8, 16, or 32 within the FLL block, it’s complicated but useful, the MCLK is for inner system and CPU, while the ALCK and SMCLK will offer a time module to peripheral module and provide a time standard.

tips: I think learn some FPGA and digital circuit knowledge will be helpful to learn this graph.
Anyway, the time module is the basic requirement for the communication of a digital equipment with other equipment, even the protocol deal and port are important, today we just know enough about the time.

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