October 1985
OCTOBER
1985
October 11th, 7:30 PM Next meeting: November 8th, 7:30 PM Meeting: November Elections will be held at this Notice: meeting, try to make it! I f you have someone to nominate (especially for editor--st ill unfilled) contact one of the following: or Glen Kirschenman n 786-4790 434-5254 Dirkson Sherm Bob Floyd Bruce Haug Frank Haug Jim Schulz
. . . President . . . Vice-Pres . . . Disk Lib. . . . Paper/Ed. Lib.
487-2627 Jon Nelson Edi tor Max Feuer. 774-6226 Treasurer 774-6226 Bruce Haug Cass Lib. 537-5442 Steve Pauley Secretary SPACE/TAI G Bu 11 et in Board 473-2897
Paul Published by the St. Enthusiasts Computer Atari independent an (SPACE), business no with organization Atari with affiliation is Permission . Incorporated similar any to granted organization with which SPACE to newsletters exchanges this in reprint material however, nev..1sletter. !.,.le do, to the asK that credit be authors and to SPACE. those Opinions expressed are of the article authors and do the not necessarily reflect club SPACE, of views or Atari officers, members, Inc.
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484-9027 483-3895 774-6226 560-2917
AT THIS MEETING: OUR ATARI REPRESENTA TIVE CLUB OFFICER ELECTIONS FEATURES IN THIS ISSUE: PART IV OF CHRIS CRAWFORD'S ASSEMBLY LANGUAGE COURSE
PART I OF A DOS TUTORIAL FROM A REMOTE SPACE MEMBER THE MEANING OF ATARI FROM ANOTHER SPACE MEMBER A Sl.H1ARY OF OUR VISIT FROM BRODERBUND ATARI 260ST SPECS.
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BYTES FRIM THE PRES, by Bob Floyd Atari Rep at Ntetiag - The local Atari manufacturing representative, Charlie Devine of Continental Merchandising, will be at this meeting to dmo ST software and answer our questions, A few of you left questions with me at the last meeting, which l have passed along to Charlie. Feel free to ask him other questions at the meeting, especially if they are related to XE, XL etc., since these could bt missed with all the ST excitment. I have asked Charlie to dmo the MIDI capabilities of the ST, but l don't know if he'll be able to do this, What about the XE/XL? - It has been brought to my attention that the club is paying too much attention to the ST and not enough to the XE/XUSOO (8-bit) series, Since only a few ambers have ST's, we really should spend most of our time on the 8-bit ccnputers, Unfortunately, most of the news has been on ST's and the October meeting will be heavily ST oriented, So, we should be more 8-bit oriented by Novmber, I hope to help out on 8-bit in the Beginner's Group once l relinquish presidency. Ustr Friendly - User Friendly Cmputers bas changed owners, The are very friendly and have a large mount of Atari software and hardware for both 8-bit and ST series, User Friendly also bought out the Schaak inventory of Atari software and is selling it at $1 ,00 for cassette programs and $2,00 for disk and cartridge progra11s, There are sme good oldie-goldits there, They are also now an authorized Atari service center, Incidentally, Phil Seifert is now at Wizard's Work. What' Happening? - SPACE and TAI& are selling Happenings books at the October meetings, These art the large 2-for-1 coupon books that many people purchase, We will have a listing posted at the meeting of retailers in the book, Joanne and I always buy one each year and easily get our money's worth on movies alone, See Joanne at the meeting to buy a book, Price is $14,50 - this is $2,00 less than suggested retail, The club will make a small profit on each one sold, BBS - The BBS is up again, but on the old Form software, A 130XE is being purchased by TAI& thru Wizard's Work at cost for the BBS (thanks Phyllis!), The switch to BBS Construction Set software will be made once the 130XE arrives. Hise. - We received a disk back frm Atari Cmputer Club of Denver in response to our mailing to thm. We will make these programs available in the near future. J have purchased another book on •c• programming for the club, Jt is 'Prograining inc• by Stephen P. Kochan and is easier for the beginner, There are aore examples and sample programs, Also, l think 1 King Tut's Tmb 1 frm Antic Magazine is one of the best bargains around, and for a reasonable price, Jt is basically a clone of the arcade game Tutankaaen, It must be mail ordered frm Antic,
Septt11ber Meeting Minutes By Joanne Floyd
The last SPACE meeting was held September 20 with 85 people present. During the President's report, Bob Floyd thanked Gordy frm Wizard's Work for arranging with the University to keep our present meeting rom. With regard to recent nNs/r1111ors 1 he noted that the software cmpany Datasoft has gone out of business. He also rec0111tnded buying printer supplies at the Cmputer Supply Store, noting that the store now bas colored paper in stock, During the Vice President's report, Bruce Haug said that the plan to purchase a ribbon re-inker is moving forward, The re-inker machine requires different adaptors for different types of ribbons, Which adaptors are purchased by the club will depend upon which printers are owned by interested club ambers. (If you are interested in this service and have not contacted Bruce to give him information about the type of ribbon you use, please do so at the next meeting,) Bruce also discussed the article in the last newsletter on •c• progrnting language, A •c• language cmpiler is available for purchase frm the club, but people will need to read a book to figure out how to use the cmpiler, Bruce recmaends a book by Brian W, Kernighan and Dennis M, Kitchie called The C Programming Language, Nax Feuer, the treasurer, reported that the club's bank balance is $790,76 (ainus outstanding bills) and that the aeabership count is about 100. Dick Johnson, president of TAJ&, reported that the TAJG-SPACE bulletin board will be down until a new BBS system is put together using the recently purchased 'Bulletin Board Construction Set•, Dick also announced that he is interested in starting an ATARI ST group. Under old business, Bob announced that the C18'utt ATARI user's group SPACE has purchased 110St of our disk library and will independently distribute those dists to its members, Under new business, the nminating c-ittee, which is responsible for lining up candidates for t•e November officer elections, was appointed. Shera Erikson and Glen Kirschenmann volunteered to serve on this cmai ttee, At the end of the meeting, Bill Holt, a representative of Broderbund software, dmonstrated Printshop, Stealth, and Whistler's Brother, (He held several drawings during the course of his dt11onstrations, giving away these three programs as well as Loderunner's Rescue and Spelunker,) Bill also gave sme background information about Broderbund, noting that aost of their programs are written not by software developers but by individual users, He also made the point that Broderbund will be unable to continue to support ATARI if the present level of progrilll piracy continues, since software cmpanies don't aakt as much profit as we assume they do, With regard to new products, he mentioned that a Print Shop Cmpanion is cming out with new fonts, new borders, and other features, and that a total of 4 graphics library disks will be available, A new Print Shop is also being developed which wilt allow capabilities such as viewing and editing cards, saving cards, putting 2 graphics on one side of a card, and putting graphics on the inside left of a card, New ST progra11s wilt include a Print Shop version frm Brodtrbund and a spreadsheet and adventure texts frm Synapse, <Broderbund recently acquired Synapse but did not take over product development,)
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Hisstd by sent people btcaust tht 111eting was running twas a d111onstration of Cmputtr Eyes, a dtvict for tht which can capture any picture cming into 1 Xls, and XEs your vidto source, (Tht harditart plugs into joystick ports 1 and 2,) The SillPlt pictur,s shown wr, il1pressivt for their clarity and dttail, The device was dtvtloptd by TAI& 11111ber Ji11 Btr,aan and is nm being 11arktttd, Ht was offering the harditar,-softwart package to club 11tllbtrs for a discounted price of ♦ 109,95, ~LOG 0,0,H, Bob &Joann, Floyd Wt will have Analog Cmputing 11agazint disk for issue 135 at the 11!1ting, Price is $4,00 for registered Analog subscribers, It arrived 1 day after the last 111,ting, Apparently, the arrival will be a little unprtdictablt, The disk now cents with a 11,nu program so that it will autmatically boot up to the menu, DOS and DUP are also on th, disk, Wt will have a set of 1 gtntric 1 directions to hand out that will bt for all future Analog disks, · Stt Joann, to purchase the disk, Also 1 you 11ay ordtr back-issues fr111 110 on up. What don 'Atari' Htan?
by Yoshio Satoh When I first heard the word 'Atari' a few years ago, I thought the cmpany 11ust be Japanese, However, I was not correct. According to what I have read, the nw was chosen since there are many Japanese ccnpany nws which sound like Alltrican (such as Sony, NEC, Panasonic, etc.> and Atari liked the opposite. It would probably be true that it is the only gtnuine Alltrican ccnpany which name came frcn the Japanese language. The word 'Atari' in Japanese 11,ans 'hit' as in 'a big hit' of a record alb111, It is a synon111 of 'success', Also, th, word is us,d to 11ean 'bite' as in 'l'vt got a heavy bite' in fishing, Atari's logo was 11ade as the shape of Ht. Fuji, And the 11our: e ~ 's na111e 11uns 'no two', or 'no other can ccnpar, with this'. Ht, Fuji is the highest 11ountain in Japan (3 177611,ttrs), Atari s1111s to have been proving the 11,aning of its name frcn the birth of the Atari 800 to the new Atari superb ccnputers with incredible prices, When I decided to purchase IIY own cmputer about two years ago, I felt a 'heavy bite' frm Atari cmputtrs' outstanding graphics capability for the price, as well as their other features as full-fltdgtd cmput,rs, Since then I've been tnjoying drawing a lot of pictures on the 1V screen with 11y Koala Pad and also getting a lot of htlp frcn productivity-oriented software including word processing and database programs, I hope Atari also 11,ans 'favorite partner' to you. Hay Atari and SPACE live long!
8RODERBlNO VISIT by Bruce Haug, VP I did not take notes to write a report on the presentation giv,n by Bill Holt frcn Broderbund at our last 111,ting, Her, art a few points of infomation that stuck in 11y 11ind 1 and I think they should be repeated, 1, 85% of the progr111s produced by Broderbund are sulllitt,d by people outside the cmpany--most of these people btlong to USER GROUPS, 2, PROGRf11S sulllitted must be original ideas, be creative, and be cmplet, with documentation etc. The most i11portant point Bill 11ad, 1 in 11y opinion, was "If you like a progr111 - write a letter•, Now if you dislike a particular feature or mode of operation of a progr111, "Hort of a reason for you to write a letter•, Print Shop is being changed because of these letters. When you write be sure you mention you belong to a 'USER" group. "USER' groups do have a say in the direction a software ccnpany develops new software, let thm know what you would like to s,, in new programs, What about other software cmpanies, write th111 also, tell thm the s111, things, Be sure to write thm if you see a progr111 for a cmputer other then ATARI and you want this program released for the Atari!-YOU can make this happen!! 1'111 sure there were other good points that Bill Holt made, that joggled the minds of a11 of you, but the it111s listed above 11ade 111 think of ALL SOFTWARE ccnpanies. After a11 Brodtrbund came to St. Pau1-f1pls to talk to ATARI ! not IBN, C0111odor,, Apple, or others, They know we are i11portant - Lets shew th111, and other software Cmpanies we art IHPORTANT.
o.o.H. News by: Frank Haug You people are 11aking 11y job aJot harder than it nttds to bt, SPACE has scnething Jikt 100 11t11btrs, so you'd think that SIJ1EBODY could donate a progr111 to the 0111, CCIII on peoplt,wt can't trade for other programs if wt have nothing to trade with, Thanks again to all those who have donat,d programs in the past, This 11onth's disk is an auto - booting disk, IT WILL NOT WORK WITH BASIC IN!!!!! Those of you with one of the Xl's or an XE should hold down OPTIIJ,I, The 11,nu uses the joystick and trigger to select and execute the programs. Nm on with the programs on the October 1985 D,O,H, I.SHUSH - You must climb to the top avoiding or 111ushing the creatures on the ledges, As you climb you will pass objects like lunch boxes and the likt, Picking these up givt you extra men, 2,FROGGIE - Get your frog into its bunker across the street and the river. 3.CH111PER - Eat all the dots avoid the 11onst,rs 4.ROlNOUP - lasso a11 the catl,, don't Jet three gtt past you and don't forgtt the black calves. 5,XEVIOUS - Shoot a11 the peoplt cars and gold targets that you can in thrtt passes. 6,NORDIC - Ski to the bottcn as fast as you can.
-4260ST Speculations by Bob Floyd Perhaps sme of you are waiting for the 260ST or 260STD to arrive before buying an ST, Here are a fN things that I have figured out and I think are probably true, Originally, the 520ST was going to have an output for television sets, ~ou can see this chip in a photo frm Antic nagazine a ft\11 nonths ago, This chip was only incorperated in the pre-production nodels of the 520ST, I think when Atari started to consider what to do for an even lower priced ST, they to drop the TV output frm the 520ST and include it in their 260ST/STD so people could get into an ST system for the lowest possible price (i ,e., without nonitor>. So, here are a ft\11 considerations for those thinking of buying an ST: 1, The 260ST/STD does not cme with a nonitor, but will work on a TV. However, it will probably only work on your TV in the lowest resolution (320x200>, 16 color graphics node. This only allows 40 colunns of text and nay not be what you had in nind for your ST, but will be incredibly superior to TV graphics fron your 8-bit nachine. However, you can still buy a nonitor to hook up to the 260ST/STD. Thus far though, you can only separately buy a color nonitor frm Atari, and it appears that the nonochrme nonitor is smewhat a special beast, So, don't count on being able to get a nonochrone nonitor. 2. The 260STD will have a built-in single sided nini-floppy disk drive, This is an advantage for desk layout and useability (the drive connector cords are too short on current outboard drives), The disadvantage is that if your drive needs servicing, the cmputer goes with it. Of course, if you only have one drive, it hardly natters. Incidentally, a 520STD with built-in double sided drive night be a very interesting product if Atari were to consider it. 3. The 260ST will have the operating systen in RIJ1 frm the beginning. Eventually, the 520ST will also, and old nodels will be able to be upgraded. However, what if you want to load an alternate operating systen? (I know this is unlikely), The 256K nenory of the 260ST/STD nay prove to be inadequate. <However, l'n relatively sure that we will see some nenory upgrades available for both 520ST and 260ST/STD in the near future. The runor is of a 2 negebyte RAN cartridge of scne sort. The reason that nore nenory nay be desireable is that BASIC is very big and with TOS in RAN also, there isn't nuch nmory left, Perhaps BASIC could be put on a RIJ1 cartridge - that would be nice,) 4. Here is a synopsis of the graphics nodes: - High-res (640x400) nonochrone for the nonochrcne monitor only. - Hedi1J11-res (640x200) 4-color for the color nonitor only, - Low-res (320x200) 16-color for the color nonitor or, if you have a 260ST/STD, for a TV, too. 5. The ST's, both 260 and 520, are configured for Epson, the new Atari printers and Epson conpatable printers. This neans that the operating systen expects to see one of these
printers when doing a screen dunp. You can still use any printer that your particular software·pernits. word processors allow you to set up codes for your particular printer. It is only for screen dunps that you nay wish to have one of the printers listed above. Hy new Epson LX-80 works very well on the ST for screen dunps, supports near letter quality text and was reasonably priced, I hope this has helped scne of you make your ST decision, There is a lot to consider fron this, plus your financial situation, USING DISKS WITH BASIC (FOR THE CURIOUS ~LY) By Chris Copeland PART I
One blustery winter day last Novenber I was playing Wizard's Revenge (fron APX> and accidently pushed the BREAK key, I was astonished to find that the progran was written entirely in BASIC. It used the disk drive to look up all sorts of responses to connands typed in from the keyboard, nuch like Zork. How could you do sonething like that using BASIC? Unable to resist the challenge, I plunged into the progran, got out ny DOS manuals and books, and cane up with the following conclusion: I needed help! Fortunately for ne, there wasn't any auailale, so I learned all about the BASIC disk cmnands on ny <Mn, This series of articles is for those who don't have tine to figure it all out themselves, but would like to use the disks in their own prograns. It's easy, just read on and type in all the examples, Let's start like I didwithout any explanation beforehand, let's look at a program that will read a filt fron the disk. First the progran, then a 1ine-by-lint explanation: 5 RBi PROGRAM 1 10 DIN Af(111):TRAP 60 20 OPEN 11,4,0, 1 D:FILENAHE 1 30 INPUT 11 1A$ 40 ?A$ 50 GOTO 30 60 ?'END OF FILE' 70 CLOSE 11 Line 10 dimensions A$ and tells the conputer to expect an error when it reaches the end of the file. Line 20 OPENs the disk file for reading, Hore about that later. Consider it the equivalent of pulling out a drawer of a card file, going to the beginning of the drawer, and getting ready to read, Line 30 INPUTs a line of text (called a record) fron 1 D:FILENAHE 1 and puts it into A$, Note: a record can only be 110 characters long. A paragraph of text fron a text file is usually longer, so you can't read nost text files with this progran. There is a way, but it's not nearly as much fun as this. Line 40 prints the record. Line 50 goes back for another reco~d. Line 60When the conputer reaches the end of the file, an ERROR136 occors. Of course, this wasn't a nistake, we expected it, TRAP 60 in line 10 told the cmputer to skip to
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ne 60 in the event of an error. Take out th, TRAP if you nt to see this yourself. ne 70Ny 110ther is always telling 11t that if you break smething, fix it, if you use smithing, put it back, if you make a miss, clean it up •• , Well, we opened s•thing ••••
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That wasn't too hard. This time let's write to a disk file recordbyr1tord:
channel to. Valid device na11es are C: (cassette>, D:FILE (disk>, K: (keyboard>; and a bunch of others. The value placed in the ce111and para11ater tells the cmputer what tYPt of operation is to be perfom,d. The cC1111nds ustd with drives fo11c.. Tht s111t n111bers can mean smething else to another peripheral. 4 opens the IOCB for reading only. We already used it in one exaap le • 6 is very useful. It optns the disk directory (use it with tht fil1n1111
5 REN PROGRAN 2
10 OPEN 11,e,0, D:NYFILE" 20 ? 11, "Record niaber one• 30? 11,"The Second Record' 40? 11,'You can put anything in a record!' 50 CLOSE 11 1
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Line 10Open the file for writing. Again, more on this later, One word of warningdon't use a filen111e that's already on the disk or it will be deleted, Lines 20-40 Nc. we wite smething to the file. Line 50Never forget! If you have a word processor like AtariWriter or Speedscript 3,0, take break to load the file we just created. That's what it looks like,,, just what we told it to do. If you don't (even if you do>, go back and type in the first progr111 (Do you think I actually beleived you would type it in?> and try reading NYFILE (change line 20), For those of you too lazy to tyPe all that in, you're missing all the fun! N<M try the fo11c.ing changes to the last prograa1 REN PROGIWt 2,5 5 DIN A$( 111> 20 ?1 >1 ;:INPUT A$ 30 IF AS= 1 Q1 THEN 50 40 ?11,At - and use progra11 1 to read what you type, INPUT in line 20 works like it does in regular BASIC. Ready for sme more? Ltt's take a look at the OPEN ce111andwhat it does and h<M to use it. Without g,tting too t,chnical, I will try to explain h• it works, Whenever your Atari cC111unicates with a peripheral, it OPENs one of its eight JnpuVOutput Control Block (IOCB>'s, Think of each JOCB as a channel to a peripheral. They are used to c•unicate with disks files, the printer, mod11s, the screen, the keyboard, or any other per ipher a1. The IOCB's are numbered frm O to 7. IOCB 10 is used for the screen editor, it can't be OPENed or CLOSEd frm BASIC. JOCB's 6-7 are used for other things like CL~D and graphics. The others (l-5) are reserved in BASIC for your USI,
When you open an JOCB, you must tell the cmputer: l) Which channel you want to open 2) What you want to open a channel to. 3) What you want the channel to do (read, write, or sme cmbination of the two> Let's look at the BASIC OPEN stat11ent: OPEN lx,ce111and,0, 1 devic1:filen111t (disk only)• •x• in the exanple above tells the cmputer which IOCB to open. The last parmater tells which device to open a
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8 opens the IOCB for writing starting at the beginning
of the file, It creates a file if 1 FILEtW1E 1 doesn't already exist, or deletes it if it exists and is unlocked, OPENing locked files for writing returns an ERROR167. 9 opens the file at the end for writing, so whatever you PRINT to the file will be tacked on to the end, This can waste disk space if used too often, as every 1 append 1 (as it is called>, takes at least one sector. 12 is used to open a file for both reading and writing, Again, these numbers mean different things when used with other peripherals. Sme ce111ands can't be used with sme devicesyou can't read frm the printer or write to the keyboard. Here we are only concerned with disks, As I said before, when you OPEN a file, you HUST CLOSE it. If you don't, it may not appear in the directory, not all of your data will be written to the file, and all sorts of other yucky stuff can happen, You can't OPEN a file twice, either, OPEN it, do your stuff, and CLOSE it. Nc. that your curiousity about has been raised, 1'11 leave you until next month, when we'll discuss two ce111ands that can make your disk drive really work for youNaTE and POINT. Until then, experiment with these c•ands and see what you can cme up with.
NfTJC PUBLISHING INC,, PERNISSIIN.
COPYRIGHT 1985,
REPRINTED
BY
CHRIS CRll¥JFORD ASSEMBLY LANGUAGE COURSE - LESSIN 4: BRANCHING One of the most important ideas in cmputing is the concept of conditional execution, This is the ability of the progr111 to execute different routines depending on conditions at the time of execution, The significance of this capability is best realized by considering h<M prograas would operate in its absence, A progr111 without conditional execution would not be able to change its progra11 flc. in response to conditions, In other words, it would always execute exactly the s1111 code in exactly the s1111 order. Every run of the progr111 would follc. exactly the s1111 sequence and perfom exactly the s1111 operations. Not very interesting, right?
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To get a grip on conditional execution, we need to look at it in its simplest expression, The simplest type of conditional execution is binary in nature. We have a chunk of code; the 6502 will either execute it or it will not execute it, The decision is made on the basis of a boolean value; a true value will tell us to execute the chunk, while a false value will teil the 6502 not to execute the chunk. The basic mechaniSII for doing this is through an instruction that performs a transfer of control. This involves nothing more than altering the program counter, You may recall that the program counter is a register in the 6502 that points to the address of the currently executed instruction. When that instruction has been executed, the program counter is increased by the length of the instruction (l,2, or 3 bytes, depending on the instruction). lt new points to the next instruction, This little system allews the 6502 to step through a program in sequence, But there are also instructions that will alter the value of the program counter, alewing the 6502 to jump to another area of memory and another part of the program, The simplest of these is the JNP instruction. lt takes the form JNP LABEL. This loads the value of the LABEL into the program counter. lts effect is to make the 6502 j1111p to the address of LABEL and continue execution frm there. lt is directly analagous to a GOTO instruction in Basic, For conditional execution we need smething more, We need the 6502 to have capability to make a binary decision based on a binary value, The solution used by the 6502 involves flags, These are single-bit Boolean values stored together in a single byte of the 6502 called the processor status register <SR>. The status register is eight bits wide but stores only seven flags. These seven flags are labelled N,V, B, D, 11 z, and C. You have aready encountered the C (Carry) flag and the D<Decimal) flag, ln this chapter, we are concerned only with the N, V, Z, and Cflags, The magic instruction that makes possible conditional execution can take many forms, Jts general form is Bfv LABEL, The B stands for 'branch', The 'f' stands for a flag, and the •v• stands for the value of the flag, either true or false. Hewtver, in this case, we do not use the terminology 'true or false', lnstead we use the ttrms 'set• or 'char', 'Set• means the sane thing as 'l' or 'true', while 'clear' means •o• or 'false', The label is the address to which the 6502 should branch if th, condition is satisfied, If the condition is not satisfied, then tht 6502 will simply skip this branch instruction and go to the follewing instruction,
For example, suppose that we instruction sequence: LDA 10 BCS KAREL IA LDA 15 KARELJA STA FISH
have the
This will first load the acc1111ulator with a zero. Then the 6502 encounters the BCS ('Branch on Carry Set') instruction. lt looks at the Carry flag, If this flag is set then the 6502 will indeed branch to the label KARELIA. (For all you geography buffs, Karelia used to be in Finland,) In other words, if the Carry flag is set, the 6502 will skip over the LDA 15 instruction, Thus, a zero will be stored into FISH. Hewever, if the Carry flag is clear, then the 6502 will not take the branch, It will instead continue executing the next instruction, which will load a 5 into the accumulator, Then it will cme to the label KARELIA and store that 5 into FJSH, Thus, the value of the Carry flag determines whether a zero or a five is stored into FISH. The converse of BCS is BCC ('Branch on Carry Clear'), This will cause the 6502 to take the branch if the Carry flag is clear , There is also a pair of similar instructions for the V-flag, These are BVS and BVC. They will cause the 6502 to branch on the value of the V-flag, New the situation· gets unncessarily confusing. Tht istructions for the Z-flag should be BZS and BZC -- 'Branch on 2 Set• and 'Branch on Z Clear'. Unfortunat,ly, the dlllb designer of the 6502 thought he would g,t cute at this point, so instead he called these instructions BEQ and H, for 'Branch on Equal' and 'Branch on Not Equal', Ht nevtr mentioned what he thought is supposed to be equal to what. We're stuck with it, so make the best of it. Just remember what these instructions really mean BZS and BZC, If you think in tems of the 2-flag, it will work out just fine, If you try to think in terms of equal or not equal, your attention will be diverted frm the real truth of the matter and you may make mistakes, So keep your eye on the ball and think in terms of Z! The next pair of branch instructions use the N-flag, These are even more insidious than the previous two. They are called 1111 and BPL, meaning 'Branch on Ninus' and 'Branch on Plus•, At first glance, these appear to be reasonable substitutions for ~Sand ~C. After all, if you load th, accumulator with a signed number, and the number is negativt 1 then the N-flag will be s,t, while if the number is positive, the N-flag will be clear. Thus, it would seta that 1111 is truly equivalent to ~S and BPL is truly equivalent to ~C. This is th, source of
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/4'ny a bug in beginner's programs. Consider the follawing f~.a91ent of code: LOA SEC SBC BPL
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FISH
Suppose, for 1xa1111le, that the value in FISH is $Cl and the value in GOAT is 1. When the 6502 subtracts GOAT frcn FISH, it wi 11 get a result of $CO. Note that the highest bit of $CO is set to 1, This is the value that will go into the N-flag. In other words, even though FISH is greater than GOAT, the 6502 will not take the branch, and this code will fail. The moral of his tale is, don't take those instructions literally. They are misleadingly naed. When you see BPL, don't think 'Branch on Plus•, think 'Branch on N Clear•, Otherwise, you'll screw up scneday, By the way, the correct branch to use in the above problem is BCS, Now for a catch with the branch instructions, A JHP instruction is a simple absolute j111p -- you specify the target address and it goes there. The designers of the 6502 realized that the vast majority of branch instructions only go a short distance. They therefore decided to implement the branch instruction as a relative branch. The machine code doesn't specify the target of the branch, it only specifies an offset. In other words, instead of saying, 1 j1np there•, it says, 1 j1111p so many bytes forward or backward.' The allowable range is 126 bytts forward or backward, Thus, you can't branch anyWhere you want, only to nearby locations, lf you must branch further, reverse the logic of the branch and use the branch to skip over a JNP statemtnt.
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This code is supposed to branch to POSANSR if FISH is greater than &OAT. And indted, if FISH is greater than &OAT, then whtn you subtract &OAT frcn FISH, you will get a positive result, right? Not necessarily!
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Summary Summary
The ATR-8000 is a device that comes in three versions: one functions as an intelligent peripheral, another gives you a CP/M 2.2 computer and the third offers you an MS-DOS 2.1 computer. Version 2 also handles the functions of version 1, and version 3 can function as version I or 2. These packages are powerful and useful; lake a close look al them. Features of unit tested □ □
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Z80A CPU; 8088 in add-on Co-Power board 16K RAM in Atari peripheral version: 64K RAM in CP/M 2.2 version: 256K RAM in CoPower expansion Up lo four disk drives: 5¾or 8-inch, singleor doublesided disks MYDOS - Atari peripheral version; CP/M 2.2 - CP/M version; MS-DOS 2.1, CP/M-86 - Co-Power board
SynFile+ is a fine data-basemanagement system for use with Atari computers. It offers powerful features and is also easy to use. We'd like lo see some on-line documentation, but beyond that reservation, we have only praise for this program. System Requirements □
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Atari computer 48KRAM One disk drive
Suggested list price: $99.95 Atari Corporation 1312 Crossman Road P.O. Box 61657 Sunnyvale, CA 94089 (408) 745-2000
mfoWo Eld AtariLab
Suggested list price: Atari peripheral version, $449.95; CP/M 2.2 version, $599.95; Co-Power expansion, $1099 SWP Microcomputer Products, Inc. 2500 East Randol Mill Road Suite 125 Arlington, TX 76011 (817) 469-1181
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Here are a iew review summari es, ior more in-depth reviews oi these and about ~O other excellen t programs see your 1 ibrary.
The AtariLab Starter Set with Temperature Module is an excellent hardware/software combination for studying science. It can be used by children and adults, at home or in schools. System Requirements □
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Atari computer 16K RAM
Suggested list price: $89.95 Atari Corporation 1312 Crossman Road P.O. Box 6'1657 Sunnyvale. CA 94089 (408) 745-2000
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lt is possible for members to place 'Want Ads' in this newsletter. The ads may be for selling used hardware, used software, tutoring services, or just about anything that has to do with Atari. The rates are as follows: 6 Lines $1.00 216 Letters 1 Line .25 36 Letters The following is a 1 ist of advertising rates for vendors or individual members. Full page $18.00 7-1/2" X 10" Half page 10.00 3-5/8" X 10" Half page 10.00 7-1/2" X 5" 1/4 page 5.50 3-5/8" X 5" All advertisements must be paid for when they are submitted, Deadline for ad placement is two Mondays before the meeting. To place ad or for more info, call the editor.
St. Paul Atari Computer Enthusiasts 2589 Fisk St. Roseville, MN 55113
Meeting site: U of M St. Paul campus Office Classroom Bldg, rooms B-35 st. Paul, Minnesota
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B fi a H□mE c□mPUTEA SUPPUES 1697 E. HOYT AVE. ST. PAUL, MINN. 55106 (612)-774-6226
SSDD FLOPPYS 10 FOR SS.90 BUTTONS $.50 EA 350 TO CHOOSE FROM
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