SIC/XE Architecture

SIC/XE stands for Simplified Instructional Computer Extra Equipment or Extra Expensive. This computer is an advance version of SIC. Both SIC and SIC/XE are closely related to each other that’s why they are Upward Compatible.

SIC/XE machine architecture:

1. Memory:

Memory consists of 8 bit-bytes and the memory size is 1 megabytes (220 bytes). Standard SIC memory size is very small. This change in the memory size leads to change in the instruction formats as well as addressing modes. 3 consecutive bytes form a word (24 bits) in SIC/XE architecture.



All address are byte addresses and words are addressed by the location of their lowest numbered byte.

2. Registers:
It contain 9 registers (5 SIC registers + 4 additional registers). Four additional registers are:


        Mnemonics             Use of Register
           B                  Base register
           S                  General working register
           T                  General working register
           F                  Floating-point accumulator

3. Data Formats:

  • Integers are represented by Binary numbers.
  • Characters are represented using ASCII codes.
  • Floating points are represented using 48-bits.

4. Instruction formats:



  • In SIC/XE architecture there are 4 types of formats available
  • The Bit(e) is used to distinguish between Formats 3 and Formats 4,
    e=0 means Format 3 and e=1 means Format 4

Format 1(1 byte):

Format 2(2 bytes):

Format 3(3 bytes):

Format 4(4 bytes):

n=Indirect mode, i=Immediate addressing, x=Index addressing, b=Base addressing, p= Program counter, e=Exponential addressing

5. Addressing Modes:
To use Format 3 use of Base register and Program counter is there.

   
           Mode               Indication           Target Address (TA) 
           Base relative      b=1, p=0             TA=(B) + displacement 
           Program-counter    b=0, p=1             TA=(PC) + displacement 
           relative   

Target address is the effective address of the instruction.

6. Instruction Set:

  • IN SIC/XE all the instructions are same as that of SIC architecture but because of Floating point data format it provide Floating point Arithmetic functions too.
  • To perform floating-point arithmetic operations,
    ADDF = Add floating points, 
    SUBF = Subtract floating points, 
    MULF = Multiply floating points, 
    DIVF = Divide floating points 
  • SVC (Supervisor call) is also provided in the SIC/XE architecture to handle Interrupts.

7. Input and Output:
SIC/XE architecture include I/O channels that allow to perform I/O operations while CPU is executing other tasks. It will allow overlapping of computing and I/O, which make this architecture more efficient. Instructions such as SIO, TIO, HIO are used to start, test, and halt the operation I/O channels.



My Personal Notes arrow_drop_up

Check out this Author's contributed articles.

If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

Please Improve this article if you find anything incorrect by clicking on the "Improve Article" button below.




Article Tags :

Be the First to upvote.


Please write to us at contribute@geeksforgeeks.org to report any issue with the above content.