mix

• Is supposed to work on a computer using base-2 or base-10

words

byte

byte := the following - dependant on if we are using binary( 2⁶ or decimal 10²) - at least 64 distinct values - at most 100 distinct values - We have to assume both value limits could exist on either computer

• Leave 2 adjacent bytes for the number 80
• 2 adjacent bytes can express the number 0 through 4095
• 3 adjacent bytes can express the number 0 through 262143
• 4 adjacent bytes can express the number 0 through 16777215
• 5 adjacent bytes can express the number 0 through 1073741824
• n adjacent bytes can express the number 0 through 2⁶ⁿ

word := five bytes plus a sign, and sign := 1 bit, plus or minus

registers

There are 9 registers in MIX.

A-register := Accumulator is one word big, many uses, especially for arithmetic and operating on data

X-register := Extension is one word big, extension on RHS of rA, used with rA to hold 10 bytes of product or dividend, or infomation shifted to the right of rA.

I-register := Index registers, I1, I2, I3, I4, I5, I6 which each hold 2 bytes and a sign. Mainly used for counting and referencing variable memory addresses.

J-register := Jump register, holds 2 bytes and the sign is always +. Always holds the address of the instruction preceding the jump instruction, primarily used with subroutines.

other features

An overflow toggle, 1 bit

A comparison indicator, 3 values, less, equal or greater

memory, 4000 words of storage

i/o devices, cards, tapes, etc

Partial fields of words

The word is indexed as follows.

(0:0) - the sign only (0:2) - the sign and the first 2 bytes (0:5) - the whole word (3:4) - the 3rd and 4th byte.

(L:R) is denoted as 8L + R in the machine

instruction format

instruction format C := the operation code telling what operation is to be performed. e.g. C = operation.8 is the LDA operation.

instruction format F := holds a modificaiton of the operation code, usually the field specification. e.g. F = 11 is the field (1:3).

instruction format I := instruction specification, may be used to modify the address of an instruction. I = 0⟹ no change. I = i means we add the number in rIi to ±AA. If the result has M being larger than 2 bytes, the value of M is undefined.

instruction format A := ±AA is the address, note the sign is part of the address.

Memory cell M := To access the memory of the computer

Notation

To denote the instruction format in a human readable manner, we use.

OP ADDRESS, I(F)

Where OP is a symbolic name for the OP code.

ADDRESS is the ±AA portion and I, F are the I- and F- fields respectively.

LDA

• take the number at position R, and fill in from the right the numbers in the address until you reach L.

backlinks

• index_of_files.pd