Sequential (146) Asynchronous

https://johnchihau.blogspot.com/2026/07/take-look.html?m=1

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Ref: https://johnchihau.blogspot.com/2026/04/take-look_0452861940.html?m=1

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John: Before we start,  you might take a look at this article . https://johnchihau.blogspot.com/2026/04/blog-post_28.html?m=1  .

Me: Ok. It mention about Asynchronous. 

John: Yes,  it mention about Asynchronous. The 1st picture above is a detailed asynchronous register. I explain it. 

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1) Index = Address or Object 

2) Tag = Control bus, e.g., output availability,  falling edge trigger, Circuit selected, Clock-line chosen, Interrupt status, Step [Asynchronous],  and,  so on and on.

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Me: Ok.

John: In fact, in the control bus,  there's a data-field called Step [Asynchronous]. This field decides if the data-receiver is asynchronous or synchronous. Like this,

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Object [Buffer zone] <--- Note,  the buffer zone is in fact in the Circuit of System not in the system of GSM.

**** Circuit [GSM]

**** Clock-line [GSM antenna]

Interrupt_status [Real]

Step [Asynchronous]

Bit [1]

Data [Pending]

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John : In code, it is MOV, buffer_zone,  data.

Me: Ok.

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If (step = synchronized)

{

data = 4 bits.

}

Else if (step = asynchronous)

{

Data = 1 bit.

}

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Mov buffer_zone,  4 bits <--- Pretty fast.

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Mov buffer_zone,  1 bit <--- Pretty slow.

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Me: Being Asynchronous is very clumsy.  Every 1 bit input,  the Circuit and the Clk line need to change.

John: You must change them, Else,  the data can't be moved to the Buffer zone which in fact is at the Circuit of System,  not at the Circuit of GSM. 

Me: Oh! God. The speed of Asynchronous receiver is much lower than the speed of synchronous receiver.

John : Yes,  if you need to transmit 4 bits to an asynchronous receiver,  the receiver need a total of 4 round of "Circuit-change" and "Clock-line change. ".

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Me: Ok.

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John : Lastly,  we look at the 2nd picture.  If the data-field of step is 0, in fact,  the transistors are cut-off. 

Me: If the transistors are cut-off, it's not a Shift data-register. 

John: It's only a parallel input output register.  Every time it output,  it output 1 bit. Every time it input,  it input 1 bit.