PUBLISHED IN LIMA NEWSLETTER FEBRUARY 1989 QUESTIONS ABOUT DIJIT'S AVPC CARD GEDITOR'S NOTE: H The following text file was prepared by DIJIT systmes to answer common questions about their AVPC card. It should, however, be of interest to all TI computer users as it contains interesting information about Rave 99 keyboards, switching power supplies, and a very interesting theoretical discussion of TV and monitor resolution. AVPC QUESTIONS AND ANSWERS The following questions have been asked of us concerning the AVPC and other DIJIT products. Since most of the questions asked tend to be redundant, we have chosen the bulletin board medium as a means of disseminating the information while cutting down on our overwhelming correspondence. If the answer to your question isn't here then please address it to us in the E-Mail section and we'll add it to the list. WHAT IS THE AVPC? The DIJIT Systems Advanced Video Processor Card is an advanced accessory for the TI-99/4A. It is installed in the Peripheral Expansion Box and functionally replaces the existing Video Display Processor in the console. IS THAT ALL THAT'S TO THE INSTALLATION? No. There is a minor change to be made in the console which effectively puts the existing VDP "to sleep" and allows addressing video functions in the P-Box. No soldering is required. WHAT TYPE OF MONITOR IS NEEDED FOR THE AVPC? (BB&P Editor's note: I use a high resolution green monochrome monitor with my AVPC card with no problems at all. The resolution is more than adequate for 80 column text work. You can see every pixel of every letter, even in 80 columns. I paid $75 for the monitor and $20 for the cable to hook the monitor to my AVPC card. Color is nice, however, and if you are interested in color read on. The comments about color monitors and TVs in this article apply equally well the the AVPC card, the Geneve computer, and the Mechatronics 80 column peripheral.) It is strongly recommended that an 80 column rated Analog RGB monitor be used. Only such a monitor can legibly display 80 column text as well as present the 512 colors and advanced graphics functions the AVPC is capable of generating. See our text file "Monitors" for what's available on the market today. CAN I USE A COMPOSITE MONITOR WITH THE AVPC? We do NOT recommend it. A composite monitor doesn't have the video bandwidth nor a picture tube fine enough to display 80 column text. We did make a provision to drive a composite video monitor with the AVPC. However we had a monochrome monitor in mind not a color monitor. Frankly, the color display is terrible, not even Yamaha uses the composite video output of the V9938 in their own MSX II computer where the composite video signal is derived external to the V9938 from the R, G and B signals. HOW ABOUT A TV? Definately no. A TV is even worse than a composite monitor. WELL THEN CAN I USE THE TTL TYPE RGB MONITOR THAT IS USED WITH THE IBM-PC? No. The TTL RGB monitor requires 5 volts of digital video data to drive it and it can only display 16 saturated colors. The AVPC generates 1 volt of analog video and up to 512 colors. They are completely incompatible. WHAT SHOULD I LOOK FOR IN AN 80 COLUMN RGB MONITOR? There are two major factors affecting the resolution of a monitor, the bandwidth of the video amplifiers and the coarseness of the phosphor dots on the display screen. Most TV sets can adequately display 40 column text and have a video bandwidth of approximately 3 to 4 Mz. But if you really examine the text displayed, you will find that the characters have a very "soft" appearance, that is, the edges of the characters are not sharp and well defined like those on a printed page. This softness is due to the electron beam not switching on and off abruptly. That little bit of time required to switch the electron beam on or off is referred to as "rise time". In the ideal world this time would be zero, but in the real world even the fastest events in nature take a certain amount of time. The closer we can approach the ideal, the shorter the on - off time, the crisper the edges of the characters displayed. It can be shown mathematically that "rise time" and bandwidth are inversely related. That is, as the rise time approaches zero, the bandwidth of the video amplifiers required approaches infinity. We can rigorously calculate the characteristics of the video amplifier required by Fourier analysis, however for a quick estimate we can use a "rule of thumb": BW(MHz) ~ 500 / Tr (nsec) The formula states that the amplifier bandwidth in Megahertz is approximately equal to 500 divided by the rise time of the pixel in nanoseconds. Typical Tr for the TMS9918A, TMS9928A, TMS9929A is 50 ns. So the video amplifier bandwidth required is approximately 10 MHz. The V9938 requirement is similar. The other major factor determining resolution of a monitor is the screen of the cathode ray tube on which the data is displayed. There is generally no problem with a monochrome screen, be it amber, green or white. But the screen of an RGB display is consists of tiny dots of red, green and blue phosphors which are lit in various combinations and intensities. The glow is blended by the eye to give the appearance of the various colors of the spectrum. The size of these dots in relation to the size of the screen determines the resolution of the CRT. Two common CRT sizes used in computer monitors are 12" (320 mm) and 14" (370 mm). These measurements are taken across the outside diagonal of the tube. The width of the displayable screen for these tubes is 243 mm and 280 mm respectively. Many computer systems use 640 pixels horizontally for 80 column display by formatting the characters in an 8 x 8 pixel block. The V9938, however displays 80 columns using 512 pixels by formatting the characters in a 7H x 8V pattern. The 512 is exactly double the 256 used by the TI VDP for 40 column display and does not include an allowance for "backdrop" or overscan on either side of the computer generated image. Add approximately 90 pixels for backdrop for a total of 602 pixels displayed. If we divide 370 mm by 602, we get a dot pitch of .6 mm which is the minimum spacing between adjacent pixels to display the 80 column text. Since the average TV picture tube has a dot pitch of .6 mm, it sounds great. However, having just enough pixels to light as there are generated by the computer or TV only works on those huge TV screens used in stadiums or other outdoor displays. It doesn't work with a CRT, especially if you sit very close to it and stare at it for an extended period of time. You need about 25% more physical pixels on the face of the CRT to eliminate undesirable things like the "moire effect", the pattern we're most familiar with when we look through two window screens, one behind the other. This occurs because the computer generated image is never in perfect registration with the phosphor dots on the screen. On a 14" CRT, it's been found that .5 mm dot pitch makes for a marginal 80 column display. We recommend .42 mm dot pitch for comfortable viewing. Of course .31 mm is much better, but then the price is also much higher. There you have it then, a 10 MHz minimum video bandwidth and a .42 mm maximum dot pitch are required for a comfortable RGB monitor. We recommend the Magnavox 8CM515, which has these characteristics, as the best value. WE'VE HAD A NUMBER OF QUESTIONS CONCERNING MONITORS AND TVs FROM OUR FRIENDS OVERSEAS WHICH I WILL TRY TO CLARIFY. First of all I'd like to say that everything above relating to composite video monitors and TVs still applies. The AVPC uses the Yamaha V9938 video display processor designed for use in the MSX II computer. (BB&P Editor's note: The Geneve computer and the Mechatronics 80 column peripheral use the same video chip.) There have been very few MSX computers sold in North America. That computer system is sold almost exclusively outside of the United States. In North America the the electric utility power system (mains) is 60 Hz and 115 volts while most overseas countries have standardized on 50 Hz and 220 volts. The TI-99/4A will accomodate either power (mains) standard. It has been determined in the early day of television that the vertical scan frequency of video display devices should be directly related to the power (mains) frequency in order to reduce the effect of external electrically caused noise and interference on the video. Thus the noise interference tends to be stationary on the screen instead of annoyingly moving up or down. To accomodate the different vertical scans, TI provided two different VDPs for the TI-99/4A, the TMS 9918A for domestic use and the TMS 9929A for use in countries with 50 Hz mains frequency. The Yamaha V9938 accomodates the 50 Hz and 60 Hz vertical scan frequencies through software, a much more elegant solution. The video horizontal scan frequency of the V9938 is 15750 Hz, while NTSC is 15734 Hz and PAL is 15625 Hz. Most RGB monitors should have no problem locking on although the horizontal frequency adjust may have to be "tweeked" a little to center the picture. CAN WE PROVIDE CABLES WITH THE SCART CONNECTION? SCART is an acronym for Syndicat des Constructeurs d'Appareils Radiore'cepteurs et Te'le'viseurs, the French radio and TV manufacturers association. They devised a connection system by which a TV could be used to display peripheral equipment such as VCRs, video disk players, games, etc., including personal computers. The standard makes use of a special 21 pin connector known in France as a "peri" connector and in England as a SCART connector. The pinout and signal levels are also specified. The SCART standard has not been adopted here in the United States and the connectors are almost impossible to obtain although if the quantities justified it, they could be imported. PLEASE NOTE: As far as we know, the SCART standard covers only the connector type, signals and signal levels. It says nothing about screen display concerning resolution or video bandwidths. Therefore, just because a monitor has a SCART connector doesn't mean that it is an 80 column monitor. HOW WILL THE AVPC DISPLAY MY EXISTING PROGRAMS? The AVPC will display most popular TI-99/4A programs as usual, but much clearer when they are displayed on a high resolution RGB monitor. IS THE AVPC COMPATIBLE WITH ALL EXISTING TI-99/4A SOFTWARE? The AVPC is compatible with most popular programs, however it is less tolerant of poorly written software than the unmodified TI-99/4A. (BB&P Editor's note: A review of the APVC to be published in the March 89 issue of BB&P will include a short list of software that doesn't work properly with the AVPC.) WILL EXISTING PROGRAMS BE DISPLAYED IN 80 COLUMN MODE? No. Existing programs are displayed exactly the same way as they are on the TI-99/4A. The enhanced features of the AVPC require specific application programs to invoke them. (BB&P Editor note: See the description of Funnelweb v4.13 in 80 columns published elsewhere in this newsletter.) CAN I ACCESS THE ADVANCED FEATURES OF THE AVPC THROUGH EXTENDED BASIC? You can access some of the features such as the mouse, with drivers written by Dodd and Hoddie, also some of the graphics features with routines such as those written by Jeff Kittka. See our X-Modem download section. As other drivers become available we will post them on our BBS. HOW ELSE CAN I ACCESS THE ADVANCED FEATURES OF THE AVPC? The advanced features of the AVPC are accessed through specific application programs such as the 80 column TI-Writer editor, 80 column Multiplan etc. All the features of the card are accessible through FORTH and C as well as Assembly Language. (DIJIT Systems will have a programmers guide for sale to people who wish to program in the latter lower level languages). We have found that many of the early programs written for Myarc 9640 under GPL, especially graphics, will also run on the AVPC. IS THE AVPC COMPATIBLE WITH OTHER THIRD PARTY PERIPHERALS? The AVPC was designed to work with and be compatible with Texas Instruments TI-99/4A peripherals. Hardware and software not conforming to Texas Instruments hardware and software specifications may not work with the AVPC. .IF DSK4.C6 WHAT IS A "QI" CONSOLE? (BB&&P Editor's note: DIJIT Systems specifically states in promotional material that their APVC card is not compatible with "QI" consoles. However, use of the below mentioned "switching power supply", which is a feature of "QI" consoles, does not by itself render a console incompatible with the APVC. I have retrofitted a "switching power supply" from Radio Shack to the console I use with my AVPC card with no problems.) "QI" stands for Quality Improvement and was the designation given the last production model of the TI-99/4A, before Texas Instruments went out of the home computer business. Internally, it had a newly designed PC board on which a large gate array consolidated the logic functions performed by discrete "glue chips". Another feature was an improved switching power supply made by an offshore contractor. The latter were surplused out to Radio Shack and others and had the contractor's name "IRIICHI TSUSHIN KOGYO CO., LTD." on them. Externally, the "QI" is a beige console recognized by looking at the side accessory port. The shielding "finger stock" is silver colored, all non-"QI" consoles have gold or brass colored "finger stock". We cannot endorse the "QI" consoles for use with the AVPC because they are a rarity and we have not tested them. Besides, there are plenty of standard consoles on the used market and we know they will work. IS THE AVPC COMPATIBLE WITH THE HORIZON RAMDISK? Yes, there was an incompatibility between the AVPC and the Horizon Ramdisk. The AVPC, being the new kid in the neighborhood has received some "heat" for incompatibility. The Trade Union argument that "the last card in the box has the lowest seniority" and so should take the "heat", we found unacceptable in this case. We knew the AVPC was compatible with TI, CorComp and Myarc disk controllers and had no problems when saving Text2 (80 column) files or other advanced files to floppy disk. If you couldn't save them to the HRD, then clearly the Ramdisk was not emulating a standard floppy disk drive. The problem was in the HRD Operating System or ROS. Barry Boone came to our rescue by writing a ROS "patch" for HRD owners who also have V9938 based video systems. BARRY'S ROS PATCH really consists of two different programs, one for the TI and CorComp disk controllers and the other for the Myarc disk controller. Both are "Fairware" and are included in the download section of the bulletin board under the title: "Horizon ROS ". I HAVE A RAVE KEYBOARD, WHY CAN'T I GET THE AVPC TO QUIT WITH "[FCTN] ="? Incorporated in the power up routine of the AVPC is a little feature to eliminate the bane of the BASIC programmer. Namely, to have keyed in a long program and requiring a "+" sign, to have your finger slip from the [SHIFT] key to the [FCTN] key and watching your work disappear. Now you have to make an effort to QUIT, you must use two hands and press [FCTN], [CTRL] and "=". The RAVE keyboard only scans two keys at a time and so it can't sense our three key QUIT feature. However RAVE does sell a cable assembly for their keyboard which works like the reset button on the "Widget" and accomplishes the same thing. WHY DON'T SOME OF THE "FAST-TERM 80" FUNCTIONS WORK WITH THE AVPC? "Fast-Term 80" started out being an experimental version of Fast-Term called "Fast-Term 9640" by Paul Charlton. According to the documentation, he admits that it was a trial version. It was made usable on the AVPC through the prodigious efforts of some local programmers working without source code and not asking for remuneration. If it has flaws, sorry about that, maybe Paul Charlton will fix them if he has enough requests. DOES TELCO WORK IN 80 COLUMNS ON THE AVPC? Yes. Charles Earl, the author of TELCO, has or had in his possession an AVPC via Bob Boone of the Ottawa Users Group. TELCO Version 2.1 was released to take advantage of the new 80 column capability of the TI-99/4A. In general the program works beautifully although there are a couple of minor flaws that we're sure will be taken care of, in time. TELCO is a complex program and was written in modules or overlays so that it could be accomodated with the limited memory available in the TI-99/4A. The basic 99/4A can only hold 3 of these overlay modules in memory at a time and so as a new function is requested the program must go out to the disk and retrieve that overlay. Mr. Earl has ingeniously taken advantage of all the video memory available with the AVPC and stored 27 overlays in it. In effect it acts as a "RAMDISK". And so the execution of TELCO with the AVPC is substantially faster than on the basic TI-99/4A. TELCO Version 2.2 is now in the X-MODEM download section of the DIJIT systems BBS. DOES THE AVPC HAVE PROBLEMS WITH SOME TERMINAL PROGRAMS? The AVPC had problems with interrupt driven terminal programs such as TE II, Fast-Term, Mass Transfer etc. Non interrupt driven programs such as OMEGA work fine. After a month of self doubt, we discovered the problem wasn't our doing after all, but that there was a "bug" in the RS-232 card. See below. If the EPROM in the RS-232 card is replaced, the AVPC works with all terminal programs that we are aware of. WHY DOES THE AVPC HAVE PROBLEMS WITH THE RS-232 CARD? The AVPC was designed to work within the hardware and software constraints of the TI-99/4A. To do so required sharing the external interrupt bus between the P-Box and the console. This incidently, is one of the major differences between the AVPC and the Mechatronics 80 Column Card. The RS-232 card was the only card made by TI or third party vendors that made use of this external interrupt bus until the AVPC came along. There is a "bug" in the TI Interrupt Service Routine that causes the card to shut down when an interrupt is sensed but there is no data in the incoming buffer. CorComp and Myarc copied the ISR and the "bug" with the same results. If TI stayed in business and had brought out any more interrupt driven peripheral cards, they would have had to contend with the ISR "bug". DIJIT sells code correction EPROMs for the TI, CorComp and Myarc RS-232 cards. WHAT IS "FAST VIDEO RAM"? The AVPC was designed not just to display computer text and graphics on the screen, but to work with "real time video frame grabbers" and other digitizers. For this reason Yamaha recommended the more expensive 120 nanosecond fast video RAMS. Some brands of 150 nsec RAMs will work just fine. However we found that some, notably the TI 4464-15 does not work. CAN I USE THE AVPC'S EXTRA RAM FOR OTHER PROGRAMS? (BB&&P Editor's note: The AVPC card usually comes with 128K of VDP ram and has sockets for an additional 64K of VDP ram. This replaces the 16K VDP ram that comes with the console. This extra video ram is partly why the AVPC card can display up to 512 colors and can easily show text in 80 columns.) The CPU cannot directly access the AVPC's RAM and so cannot run programs out of it. Video RAM can be used as a buffer to store data, however. As explained above, TELCO does just that and stores its modules or overlays in video RAM, in effect making it work as a RAMDISK. Access to video RAM for data storage can only be had through Assembler or other low level languages. WHAT IS GENLOCK? The term "genlocking" is a contraction of "general locking" and refers to the complete synchronization of a video accessory with an external video source. Genlocking is required in order to do superpositioning of graphics or other video, on the source video also for digitizing. In a TV studio, all cameras and special effects devices are synchronized by a standard clock signal that is distributed throughout the studio. However when such a standard signal is not available, it is necessary to derive the synchronizing information from the source video by means of a genlocking device. The name "Genlock" has been applied by Amiga to an accessory capable of superpositioning or overlaying computer graphics and text onto externally supplied video. WHAT IS A 'REAL TIME FRAME GRABBER'? It is a video digitizer that can capture a video image as fast as it is presented. Some video digitizers in use today, notably on the Amiga, cannot capture live video. They work by slowly scaning a picture in monochrome through color separation filters and storing it in memory where it may be manipulated for the purpose of screen display or dumping to a printer. A television image consists of 2 'fields' interlaced together to form a complete picture called a 'frame' which is equivalent one picture of a movie film. Each field requires 1/60 of a second, the total frame then takes 1/30 of a second to display. I countries using the PAL standard, a field requires 1/50 of a second and a frame is 1/25 of a second. Our DIJIT-EYE-ZER will be capable of capturing either a field or a frame in 'real time', as quickly as it is displayed. And we will be able to do it in 256 colors in medium resolution mode. (BB&&P Editor's note: The DIJIT-EYE-ZER will be demonstrated Feb 18-19 at the TI-FEST WEST 89 in San Diego CA.) DOES THE AVPC WORK WITH THE BUD MILLS 32K CONSOLE MEMORY EXPANSION KIT? We have not had any complaints on that from our customers. Barry Boone claims to have no problems with it and his Mechatronics card. We will maintain a conservative wariness on this one because it gets its speed increase by eliminating the 'wait states' that TI had built in to assure timing compatibility with peripherals. .PL 1