assembler

to the operating system

∎ Data transfer (RD, WD)

∎

A buffer is used to store record

∎

Buffering is necessary for different I/O rates

∎

The end of each record is marked with a null character (00)16

∎

The end of the file is indicated by a zero-length record

∎ Subroutines (JSUB, RSUB)

∎

RDREC, WRREC

∎

Save link register first before nested jump

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A simple SIC assembler

∎ Assembler's functions

∎ Convert mnemonic operation codes to their machine

language equivalents

❖ Convert symbolic operands to their equivalent machine

addresses

∎ Decide the proper instruction format

∎ Convert the data constants to internal machine

representations

∎ Write the object program and the assembly listing

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Difficult

∎ Convert symbolic operands to their equivalent

machine addresses

∎ Forward reference

∎ 2 passes

∎ First pass: scan the source program for

label definitions and assign addresses

∎ Second pass: perform actual translation

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Example program with object code

(Figure 2.2 pp. 47)

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Example program with object code

(Figure 2.2 pp. 47)

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Example program with object code

(Figure 2.2 pp. 47)

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Format of object program

(Figure 2.3 pp.49)

∎

Header record

Col. 1

H

Col. 2~7

Program name

Col. 8~13

Starting address of object program (hex)

Col. 14-19 Length of object program in bytes (hex)

∎

Text record