2 Welcome to another batch of 8-bit's technical tips. These pages are not just for hardware problems but also software and programming difficulties. Send your problems to: Andy Nibbs Andy Nibbs Tech-tips Tech-tips 2 Seaview c/o Duncan WebsterHoylake 7 Ashdale Wirral Thringstone, LEICSL47 2DD LE6 4LW I am told by Duncan that the response to the last episode was good, thanks toall of you for that. If at any time you feel you do not totally understand Tech-tips or want something explaining, do not hesitate to drop me a line. In this edition of Tech Tips Master Compatibility Envelope programs View spellcheck dictionary size Adventure creators Watford solderless RAM Producing animated digitised pics Subject: Master Compatibility. One of the most simple problems with master compatibility to solve is one of the most complex to explain. CHARACTERS Most things printed on your beeb's screen are characters these include all letters, numbers and symbols. USER DEFINED CHARACTERS These characters can be altered and so made to look entirely different to how they did before with a command in a program. BBC B software developers defined the characters from 224 to 255 as shown in the user guide but unwittinglystart PRINTING their defined charactersfrom ASCII 128. This works fine on the BBC B but on theMaster when the program prints characters from 128 the Master prints not the characters from 224 but the characters from 128. CURING THE AILMENT: (1) Modifying the program not to print characters 128 onwards but 224 onwards. (2) Using the ACORNSOFT CONVERT ROM on the welcome disc. This does about the same thing. Subject: Envelope designers A sound envelope designer was featured in BEEBUG MAG a really long time ago. I'm too lazy to look through back issues but maybe some reader has that mag to hand. Maybe somebody could writea similar program for 8-bit software! Subject: View Spellchecker A PD program by Alan Blundell R.Pashby wanted to know what is the largest dictionary file available on the 32k BBC B. The answer is, as big as you filing system can handle: DFS: Just under 200K (80tracks) Just under 100K (40tracks) ADFS: Around 600K (ADFS 80TDS) Some alterations to the program do have to be made to allow such large expansion. Refer to the manual for details of this, any problems drop me a line. He also mentioned the dreaded Can't extend error. CAN'T EXTEND This error is produced when the DFS tries to add data to a datafile and there is not enough space on the disc immediately after the file to accomodate the extra data. The trouble is, when the computer is first instructed to OPENOUT a new file for writing to it gets the largest space on the disc for this file. Normally this is the last file on the disc and so CAN EXTEND to the end of the disc. But, if a file is saved after the file which will be extended, extending the file would overwrite it. So it can't extend! Well done to reader 1K1 for supporting Liverpool, I do too! CAN'T EXTEND, THE CURING OF: If you stick to having one disc for the Spellcheck programs and datafiles and you regularly perform a *COMPACT command on this you will not suffer from this program. Subject: Watford solderless SWRAM + Yorkshire boys discs. As I do not have access to, or any experience of this board I am asking other readers to write in. However you should check: a) You do in fact have any sideways RAM installed, I am not sure that this is supplied with the board. If you do not Watford will sell you the RAMs. b) Any READ PROTECT or WRITE PROTECT switches are turned OFF. Subject: Adventure Creators Since way back there have been several adventure creators for the beebs GAC from Incentive software, The Quill, and (I think) a beeb version of ALPS (which pre-dated the Arc version). You could probably get a copy of any of these through classified ads in 8-BIT and other mags. I am at the moment submersed in the rigours of writing my own creation system and a manual for it. More info on that as it develops. I'll probably use it to write some adventures for 8-BIT PD. SOUND SAMPLING You may have noticed that in the August Micro User there is an article about using ATARI ST samples. You could probably use the LOG conversion program on output from a sampler attached to a Beeb. Hello to Dave Stillman. Subject: Animated Digitised Pictures Perhaps the first place to start when doing these is to obtain a digitiser, the Watford Beeb Digitiser appears to be the only suitable one on the market but if you have a friend with another computer (eg Arc) and a digitiser it might be possible to convert screens. Watford Electronics advertise in BBC Acorn User and The Micro User, the digitiser is about £120. Maplin Electronics also produce a videodigitiser kit which could be interfacedto the Beeb, but you would have to interface this and write software for it to get a working digitiser. Maplin catalogues can be bought at WHSMITH stores around the country, the kit is quite cheap at around £35 though extra expenditure would be involved in interfacing etc. Certainly the right option for the person who can write machine code and is prepared to spend time building and writing software for it, but has a limited budget. VIDEO DIGITISERS A video digitiser is a device which converts video signals into digital data to be processed by computer. Video digitisers on the beeb are limited by the beeb's lack of good graphics, compared to PCs, ARCS Amigas etc. The whole 8-bit range of BBCs are woe- fully short of one commodity vital for any animation especially digitised pictures, MEMORY. Some compromises have therefore to be made. You're never going to get full` screen, 25 frames per second animation on the beeb, or most other computers for that matter. For example, in the star wars animationdemos, which don't use sideways RAM at all!, the screen size is small. The screen size and overall mode is controlled by the 6845 CRTC chip and understanding the operation of this chip is a must for anybody wanting to animate digitised pictures. CATHODE RAY TUBE CONTROLLER (CRTC) Displays on monitors and TVS (except pocket LCD TV sets) are all produced by a scanning cathode ray tube, basically this shoots little subatomic particles (electrons) at a screen of phosphor dots on you're screen which glow when hit making the a display you can see. There are dots for red, green and blue points on colour screens and three separate guns firing the electrons at these all scanning the screen producing the whole display. This cathode ray tube is controlled by one small chip, the 6845 CRTC which controls (amongst other things!): Number of characters across and down the screen, vertical and horizontal adjustments to position, whereabouts in memory the screen data starts and interlacing. Anyway you'll need The Advanced User Guide, The New Advanced User Guide or A Master Reference Manual to find the information about this chip that you will need. These books can be obtained from mail-order or from your local dealer. To animate lots of pictures you'll needto hold all those pictures in memory at once - maybe using sideways and/or shadow RAM. Then you need to switch thedisplay between the individual picturesto animate. The switching entails either physicallycopying the picture data or switching the 6845 registers to get the same effect. Only a certain amount of framescan be switched to this way as not all memory can be switched to and so you might also require some copying of memory to supplement this. DELTA COMPACTION A way of storing more frames for animation in memory at once is to store only the changes between frames. This is more complex to code but saves memory. SUMMING UP The 8-bit range of BBCS are sorely limited as a vehicle for digitised animation, but for some people this in itself is a good reason to try it. It might be interesting to see any results anybody has at this. If you need any help with any aspect of this or any other area drop me a line. If you asked a question in either issue 11 or in issue 13 any answers will be in the third Tech Tips. AJN, 14th July. Which brings me to the end of the second Tech Tips I hope you enjoyed and understood it! Keep the questions coming in! This was written and produced by Andy Nibbs using Fantastic 7 editor by Andy Nibbs on a BBC Master 128. (In case you wanted to know) Buy MasterDisc from 2 Seaview, Hoylake, Wirral, L47 2DD now!