This presentation is the property of its rightful owner.
1 / 18

# Lecture 1: SIC Architecture PowerPoint PPT Presentation

Lecture 1: SIC Architecture. COP 3402 Spring 2009. Simplified Instructional Computer (SIC). Memory: 8-bit bytes 3 consecutive bytes form a word (24-bits) Addresses are byte addresses Words are addressed by location of their lowest numbered byte Memory size = 32, 768 (2^15) bytes.

Lecture 1: SIC Architecture

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.

- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

## Lecture 1: SIC Architecture

COP 3402

Spring 2009

### Simplified Instructional Computer (SIC)

Memory:

8-bit bytes

3 consecutive bytes form a word (24-bits)

Words are addressed by location of their lowest numbered byte

Memory size = 32, 768 (2^15) bytes

### Simplified Instructional Computer (SIC)

Registers:

Five registers

Registers are 24 bits of length

### Simplified Instructional Computer (SIC)

Data Formats:

Integers stored as 24-bit binary numbers

2’s complement representation is used for negative values

Characters stored using 8-bit ASCII codes

### Simplified Instructional Computer (SIC)

Instruction Formats:

x: flag bit used to indicate indexed-addressing mode

### Simplified Instructional Computer (SIC)

Instruction Set:

Basic set of instructions, load and store registers (LDA, LDX, STA, STX,etc.), and arithmetic operations (ADD, SUB, MUL, DIV)

Arithmetic operations involve register A and a word in memory, and the result is left in the register.

Instruction COMP compares a value in A with a word in memory, and sets the condition code CC to indicate the result.

Jump instructions test the setting of CC

JSUB and RSUB instructions are used for subroutine linkage

### Simplified Instructional Computer (SIC)

Input and Output:

Performed by transferring 1 byte at a time to or from the rightmost 8 bits of register A.

Each device is assigned a unique 8-bit code

Three I/O devices instructions:

Test device (TD): tests whether the addressed device is ready to send or receive a byte of data

Write data (WD)

### SIC/XE

SIC is upwards compatible with SIC/XE.

Memory arranged in bytes (Max = 220 bytes).

Can do floating point arithmetic.

Has more registers.

Can do I/O in parallel with computation.

### Data Formats

• SIC/XE supports integers and characters in the same manner as SIC.

• Introduces new 48-bit floating point type.

• 1-bit sign bit

• 11-bit exponent

• 36-bit fraction

### Floating point format in SIC/XE

• 0 <= fraction <=1

• Exponent is unsigned. Range = (0 – 2047)

• Subtract 1024 from exponent to get correct value.

• Value of any float will be.

Fraction * (2exponent-1024)

• The sign of the number will be determined by the sign bit

### Instruction Formats

Op (1 byte)

Op (1 byte)

R1

R2

Op (6 bit)

n

i

x

b

p

e

Disp (12 bit)

Op (6 bit)

n

i

x

b

p

e

Number of addresses is larger. (220 as compared to 215).

Some instructions do not require operands.

Format 1:

Format 2:

Format 3:

Format 4:

### Formats (cont’d)

n=1, i=0: The word at the target address is fetched.

n=0,i=1: The address is used as the operand.

n=i: value at address is taken as operand. (backward compatibility with SIC when used in Format 3)

x=0,1: enables/disables Indexed mode (as in SIC).

### Formats (cont’d)

• b=1,p=0: Implies Base Relative Mode .

• b=0,p=1: Implies Program Counter Relative Mode.

• e determines whether mode 3 or mode 4 is in use.

• e=0: Mode 3 is in use.

• e=1: Mode 4 is in use.

• Base Relative: b=1, p=0

• Target Address = B + disp

• Program Counter Relative: b=0,p=1

• If b=p=0, then the address/disp field is taken as the address.

• Indexed addressing may be used with both these modes (x=0,1).

### Instructions

• Instructions to Load/Store new registers

• LDB, STB,…

• Floating point Arithmetic