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.
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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
Registers are 24 bits of length
Integers stored as 24-bit binary numbers
2’s complement representation is used for negative values
Characters stored using 8-bit ASCII codes
x: flag bit used to indicate indexed-addressing mode
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
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
Read data (RD)
Write data (WD)
SIC is upwards compatible with SIC/XE.
Memory arranged in bytes (Max = 220 bytes).
Can do floating point arithmetic.
Has more registers.
Has additional addressing modes.
Can do I/O in parallel with computation.
Fraction * (2exponent-1024)
Op (1 byte)
Op (1 byte)
Op (6 bit)
Disp (12 bit)
Op (6 bit)
Number of addresses is larger. (220 as compared to 215).
Some instructions do not require operands.
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).