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Simplified Instructional Computer (SIC). SIC Architecture. Two versions: SIC and SIC/XE (extra equipments). SIC program can be executed on SIC/XE. Memory consists of 8-bit bytes. 3 consecutive bytes form a word (24 bits) In total, there are 2^15 bytes in the memory.

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sic architecture
SIC Architecture
  • Two versions: SIC and SIC/XE (extra equipments). SIC program can be executed on SIC/XE.
  • Memory consists of 8-bit bytes. 3 consecutive bytes form a word (24 bits)
  • In total, there are 2^15 bytes in the memory.
  • There are 5 registers. Each is 24 bits in length.
data format
Data Format
  • Integers are stored as 24-bit binary numbers; 2’s complement representation is used for negative numbers.
  • Characters are store using their 8-bit ASCII codes.
  • There is no floating-point hardware on SIC.
instruction format
Instruction Format
  • All machine instructions on SIC has the following 24-bit format.

X is used to indicate indexed-addressing mode.

addressing modes
Addressing Modes
  • Only two modes are supported:
    • Direct
    • Indexed

() are used to indicate the content of a register.

instruction set
Instruction Set
  • Load and store registers (LDA, LDX, STA, STX)
  • Integer arithmetic (ADD, SUB, MUL, DIV), all involve register A and a word in memory.
  • Comparison (COMP), involve register A and a word in memory.
  • Conditional jump (JLE, JEQ, JGT, etc.)
  • Subroutine linkage (JSUB, RSUB)
input and output
Input and Output
  • One byte at a time to or from the rightmost 8 bits of register A.
  • Each device has a unique 8-bit ID code.
  • Test device (TD): test if a device is ready to send or receive a byte of data.
  • Read data (RD): read a byte from the device to register A
  • Write data (WD): write a byte from register A to the device.
sic xe architecture
SIC/XE Architecture
  • Memory: 1 megabytes (2^20 bytes)

Additional Registers

data format1
Data Format
  • The same as that of SIC.
  • There is a floating-point data type with the following format:

Between 0 and 1

Must be 1

  • The value represented by the above format is (-1)^s * f * 2 ^(e – 1024)
addressing mode
Addressing Mode
  • Two additional modes are introduced for format 3:

In format 3, if both bits b and p are set to 0, the disp

(or address) is taken as the target address. This is called direct

addressing mode.

Both modes can be combined with indexed addressing – if bit

x is set to 1, the value of register X is added in the target

Address calculation.

addressing modes1
Addressing Modes

For format 3 and 4:

  • (i =1, n = 0): immediate addressing mode. The target address is used as the operand.
  • (i = 0, n = 1): indirect addressing mode. The word at the location given by the target address is fetched; the value contained in this word is then used as the address of the operand value.
  • (i = 0, n = 0) used by SIC, (i=1, n=1) used by SIC/XE: simple addressing mode. The target address is taken as the location of the operand.

Indexing mode cannot be used with immediate or indirect modes.

example
Example

All of these instructions are LDA.

instruction set1
Instruction Set
  • LDB and STB
  • Floating-point operations (ADDF, SUBF, MULF, DIVF)
  • Register move (RMO)
  • Register-to-register operations (ADDR, SUBR, MULR, DIVR)
  • Supervisor call (SVC) for generating system calls into the operating system.
  • I/O channel operation (SIO: start, TIO: test, HIO: halt), similar to DMA.
complete instruction set
Complete Instruction Set

P: privileged

instruction

X: available

Only on XE

F: floating-

Point

Instruction

C: condition

code CC set

to indicate

result of

operation

sic programming example 1
SIC Programming Example (1)

SIC instruction sets

SIC/XE instruction sets

Use immediate mode will

make the program run faster

because it need not fetch

five from the memory.

slide23
SIC Programming Example (2.a)

BETA <- (ALPHA + INCR - 1)

DELTA <- (GAMMA + INCR - 1)

slide24
SIC Programming Example (2.b)

This program will execute faster because

it need not load INCR from memory

each time when INCR is needed.

slide26
SIC Programming Example (3.b)

This program will execute faster because

TIXR need not compare the index value

to a memory variable.

slide27
SIC Programming Example (4.a)

Gamma [] <- Alpha [] + Beta []

slide28
SIC Programming Example (4.b)

This program will execute faster

because it uses register-to-register

add to reduce memory accesses.

subroutine call example 5 a
Subroutine Call Example (5.a)

Read 100 words into the record buffer

subroutine call example 5 b
Subroutine Call Example (5.b)

Use TIXR makes this program run

faster

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