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:
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.
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.