May June 1980 - Commodore Computers

40
4O COMPUTE. MAY/JUNE. MAY/JUNE, 198O. 1980 ISSUE 4. 4.
Review:
Review:
6502 Software
65O2 Software
Design,
Review by
Jim Butterfield
by Leo J . Sca nlon
Howard W. Sams & Co., Inc.,
by Leo J. Scanlon
Howard W. Sams & Co., Inc.,
27O 270 pp. $1O.5O $10.50
This 'T'hi s is is quite quile a pleasant book; it it makes good reading.
.
The title lilie is is misleading: m g: the Ihe book deals with wilh 6502
programming rather than software design. In In fact. ract , 1I
rather r missed m the software design elements: clements: planning
memory, memory. designing data structures, and testing/
debugging g methodology are a rc important impona nt concepts s for lor be·
ginning g programmers. The book expends its s main
efforts on the subjects of o f writing code and handling
interrupts and a nd input/output inpUl/oUlpUl devices.
The book bouk is oriented o enled towards IOwards the Ih e Rockwell AIM A I M
65 microcomputer, m r, but bur not t too lOa heavily. Users of
other Olhcr systems will find it a worthwhile wonhwh ile reference
of text. The book appears a ideal for a programming
course textbook: textbook; it is well organized o and gets into
serious s programming quite quickly. quickly,
ChapterC 1I is partly historical, partly y an a n overview
of popular microprocessors and partly panly a brief plug
for the AIM A I M 65. There's a minor m problem where the
aUlhor describes Ih e 6800/6 502 famil y as cha racler­
author describes the 6800/6502 family as character
ized by b y novel memory-mapped architecture: re: in fact, ,
all microprocessors including Ih thee 8080 and Z-80
can aand do use mcmory memory mapped lIO. 1/0. And I rather
wish that the illlroductio introductionn to the 6502 had mentioned ned
its iis remarkable speed due to pipelining techniques -
a factor r that sc sets it clearly y aahead ooff the earlier
6800.
Chapter 2 gets into the 6502 instruction sel. set.
Similar op codes are grouped aand discussed together,
which helps to develop intuitive ideas of the
machine's capabilities. Numerous us examples of coding
arc are included. The slyle style is generally easy aand
straightforward, rward , but beginners will still find it it slow
going: Ih there's s a 10 lot 1 of malerial material 10 to gel get Ihrough.
through.
SSubroutines utines are covered in chapter I 4, ~,
mostly y in
terms oof f their mechanistic c characteristics. A couple
of time deJay delay subroutines uti aare rc ggiven, aand it it's nice
to to see ti liming m in g qquestions being \\'orked worked through
mel meticulously. iculo usly.
CChapters 4, 4, 5 and 6 get heavily y into coding
questions: list aand lookups, mathematicall routines,
and number-base conversion. Coding is isggiven through ughout
out, , but lhe the emphasis is is oon n algorithms: lhe the aauthor
Ulho r
is is concerned wwith the methods behind d a pa particular
a r
kind oof f computation. A rather unusuall aalgorithm is is
given for for calculating g the square rOOt root of ofan integer;
it it's rather slo slow w compared lO to standard methods, but but
readers may find it it an an interest interesting ing curiosit curiosity.
CChapter i 7 ddiscusses interrupts. In Insixteen pages,
it it's ha hard to tocome to togrips wit with h the whole qucslion question, ,
and a nd coding examples are arc cursory. ry. Chapter C 8 goes g"Oes
into to considerable detail dctail on o n two input/output chips:
the Ihe 6520 and a nd 6522.
There are a re two appendices and a an index. II found
the Iht: index rather sparse: for fur example, "relative " addressing" points you to LO page 40, bill but a more
useful discussion d ion can be found on page 55.
Coding g examples are arc written almost entirely in
assembly b ly language. This T s is is quite q u readable, ble. but b ut II
would vvo have preferred rred to see sec early y coding examples c XCl lllplcs
complete with wilh their machine language nguag-e equivalents.
s .
The Thc overall organization ion of or the t book is good, g"ood t
although a there are a rc inconsistencies within h in chapters: ( rs:
some have summaries, some somc have references, rcfe rl:nccs. and some
have neither. Chapter C r 2 has ait section entitled c ntitkd "How ': Ho\\,
this chapter is arranged"; it appears on 011 the sixth si:..: page of o f the chapter, which seems Seems odd..
..
The coding is good, but there are a rc a few errors.
On page 68. , the author suggests suggesls thai Iha t when n shifting shirting
signed numbers to the left, , the programmer ll llllcr should
arrangea to restore the sign bit in ill case it's shiltecl
ift l'd
out: O llt ; in fact, a change in the lhe sign n bit would be an
overflow ow situation and there would be no repairing
the damaged number. numbcr. Example 5-14 1 ~ ono n page 1391 :$9
should add a value e ofo f two to location Ti 22 rather
than the value e of one shown; shown: most Ill alcrl alert readers
ers
will pick this kind oi of' thing up. u HardwareH re purists
may wince at some of the terminology, such as use usc
ofr the term "grounded'' " instead or of "logic zcro" zero"
or ""low", . bul but everybodyy will understand rstalld wh;u what is
mca meant. n t.
The authorr has a conversational style and