May June 1980 - Commodore Computers

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24 COMPUTE. MAY/JUNE, I JUNE. 198O. <strong>1980</strong>. ISSUE 4. the instructions to be written in decimal form. Decimal loaders were eventuallyy replaced by hexadecmal loaders, which allowed the instructions to be written in hexadecimal form. Example I-I 1-1 shows both binary and hexadecimal forms of typical program instructions. Example I-I. 1-1. A Typical 6502 Program, in Binary and Hexadecimal Notation in Binary and Hexadecimal Notation Binary 10100101 01 00100001 11000101 01 00100000 10110000 00101011 101001100 00101100 Hexadecimal A5 21 C5 20 BO B0 2B A6 2C Hexadecimal representation is some help to the programmer because it frees him from using all those error-prone 8-bit binary numbers. Further, hex instructions do not contain quite so many digits in them, , making them somewhat easier to memorize. Unfortunately, though, , a hexadecimal number gives no hint as to the function of an instruction. Does a "es" "C5" instruction perform an addition, , a subtraction, , store a value in memory, or none of these? Even when using hexadecimal numbers, it is still difficult to program the 6502 microprocessor. Before you enter a hexadecimal al number into the microcomputer, you would first have to find the instructions, that you want to store in the memory of the 6502, on a list provided by the microcomputer manufacturer. The appropriate hexadecimal number (op code) can then be found next to the instruction. The time spent in looking up the instructions and op codes could be very costly in developing a program, , not to mention the possibilities of errors. rs. The next higher level of programming permits the programmer to write instructions in an abbreviated form, something closer to a human language, using abbreviations called mnemonics that can be correlated directly to the function of the instruction. A computer program can then be executed so that these mnemonics are actually converted to the sequence of 1*8 's and O's 0's that the 6502 can execute. The program that converts these abbreviations into machinem ~c e code (1 (l's and O's) 0's) is called an assembler, so this thIS form of programming is called assembly language programming. An instruction n that increments the X register by one has a hexadecimal form of E8 and an assembly language mnemonic of INX. Which do you think is easier to remember? Table I-I 1-1 lists the assembly language mnemonics for several 6502 instructions. ions . How does the assembler translate instruction mnemonics to binary codes that the 6502 can execute? The assembler contains a large table (the permanent symbol table) thatt contains all the mnemonics (represented by strings of ASCII charac racters) and their binary equivalents. The assembler compares the mnemonic in your program (a string of ASC II characters) to each ASC II character string of ASCII characters) to each ASCII character string in the permanent symbol table. When a "match" occurs, the assembler fetches the binary code associated with the mnemonic, and uses this value during the assembly process. Therefore, , the assembler translates the mnemonic INX (Increment X by I) 1) to E8, and the mnemonic CLC (Clear Carry flag) (lag) to 18. In this book, all example programs will be written using the standard mnemonics; using the standard mnemonics; Table 1·1. Some 6502 Mnemonics Table 1-1. Some 6502 Mnemonics Mnemonic Instructionn ADC Add memory to accumulator with Carry CLC Clear Carry flag INX Increment index X by 1I LDA Load accumulator with memory TTAX Transfer accumulator to index X these are the mnemonics that are defined ed in the literature off the manufacturers. urers. rf5 PET' MACHINE LANGUAGE GUIDE PET MACHINE LANGUAGE GUIDE MACHINE LANGUAGE Contents include sections on: GUIDE -Input •input and outputt routlnos. routines. -• Fixed point, , floating point, oint. and AsciiA number conversion. -Clocks •Clocks and timers. -BuIlt-in • Built-in arithmetic functions. -ProgrammIng •Programming hints and sugges- Hons. tions. -Many •Many sa sample programs. s_ If you are interested in or are already into machine language programming on the PET, then this invaluable guide is for you. More than 30 of the PET's built-in routines al"e are fully detailed detai~d so that the readEw reader can immediately put them to good u use. ... Available for $6.95 +.75 + postage. Michigan residents please include 4% state sales tax. VISA and Mastercharge cards accepted - give card numbet' number and exprration expiration date. Quantity discounts are available. liUUHrnI ABACUS SOFTWARE wmwmn ABACUS SOFTWARE P. 0. Box 7211 IUUilUUI Grand cira~d B~:P Rapids, i~~ ,1 ~i Michigan Ch i gan 49510
THANKS FOR THANKS FOR THE MEMORIES. - ,,,. PET ------ - . Thanks to these inexpensive Pet and TRS-80 memories and disk drives you can instantly increase your personal computer's capacity, capability and versatility. Expand your Pet. Disk Drives: Choose either double density 400k or dual head double density 800k on-line disk drive. Both with DOS operating system including 17 additional BASIC commands and random or indexed sequential access. Exceptionally fast 5.000 5,000 bytes per second (including verify) transfer speed lets you load 20k program in just 3 seconds. Model 8k must have ExpandamemTM to operate disk drives. All other models are plug compatible. 400k only 51295. $1295. 800k only 51695 S1695. Expandamem: E~ndamem "" : Lets you expand the size and scope of your programs. 16k, 24k. 24k, and 32k internal memory boards give you 8k of assembly language subroutines accessed via the USR command. 16k only 5425. $425. 24k only 5525. $525. 32k only 5615. $615. Software: Complete library available Write for details. Expand your TRS-SO. TRS-80. Disk Drive: Single density dual head 400k on-line disk drive is completely compatible with TRS-80 DOS and uses own controller completely compatible with TRS-80 DOS and uses own controller Only 51295. $1295. IMMEDIATE DELIVERY! ORDER TODAY! COMPUTHINK 965 W Maude. Sunnyvale. CA 94086 (408)245-4033 (408) 245-4033 Please send me the following. following: □ Pet DiSk Disk Dnve Drive 0 □ 400k 0 D BOOk 800k o □ Pet Pel Expandamem'" Expandamem'1' 0 D 16k 0 □ 24k 0 Q 32k □ Pet Software Sottware (InJo (Into only) Q TRS-80 -SO 400k Disk Dnve Drive o □ Name 0ol1 my nearest Computhmk Computhink dealer Total Total enclosed enclosed S __________ . _ Check or Money Order only Colli Calil Res add 6% lax tax Freight pre-pOid pre-paid In in continental US U.S. Dealer InqUiries Inquiries InVited Invited Name _______________ Name . , Adwe~ _______________ Address City State Zip_
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Look To MTU For 6502 System Expansi
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May June 1980 - Commodore Computers

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