This site was origionally started as a class project, giving an overview of different computer familes, but there are dozens of computer-history sites out there on the 'net so in this section I'm going to change course a little. The original TRS80 was introduced in 1977, followed by the TRS80 Model II in 1979, the Model III in 1980 and TRS80 Model IV in 1983. Note that the TRS80 Model II was a more costly business computer, and the model 12, 16, and 6000 are newer versions of the Model II as well, with added features. (The TRS80 Home Page) (Unfortunatly this site is long-gone, a shame, it had a ton of good info). I origionally set out to just include the I, III, and IV here but after becoming the owner of a Model II, I discovered that there is very little support for them on the 'net. The 16 and 6000 have a 68k CPU and can run lots of cool Xenix software, but because they also have the z80 they can run in Model II or 12 mode too. The Model 12 differs in that it has everything on a single board, where the model II has a passive backplain and several seperate boards. I had little luck unearthing what was actually inside one of these computers, here's what I found in mine. The backplain has serveral 80 pin card slots. These use a pin spacing similar to an ISA card, closer together than an S-100 card. There are 4 boards in my system. The first is a keyboard and video controller. Next is a RAM card. After that is a floppy controller / parallel port card, and finally a CPU and serial port card. I would like to actually figure out the pinout of the bus connection and maybe even make some hardware for the system. I'm thinking it would be nice to have ports and things in locations where a Model III or 4 program would expect to find them. I *think* the Model II has a lot in common with the Model 4, though unfortunatly you can't exchange disks between them. See the "RAM" section below for more details. More on the Model II to come! Scroll down for a little more info for the new TRS-80 user.
Processor: The TRS80 uses the Zilog Z80 microprocessor, which is capable of addressing 64k of RAM.
RAM: The original TRS80 came with just 4k of RAM, but later versions had more memory and the computer can have up 16k internally and 48k with the expansion box. The TRS80 Model III can have up to 48k of RAM. The TRS80 Model IV can have up to two banks of 64k each for a total of 128k of RAM. It should be noted that the Model IV didn't just duplicate the old systems and add bank switching, it's much more interesting. The Model I and III both have the ROM and keyboard memory-mapped in the first 16k of space. The Model IV can emulate this, or it can use I/O mapping for the keyboard and swap out the ROM for RAM, leaving the full 64k of address space free for RAM. The Model II series also uses the full 64k address space for RAM.... add to this the fact they both use the same CPU and both have similar display abilities (see those sections) and you'll see why I think they have more in common that most people give them credit.
Keyboard: The TRS80 I and III use a typewriter style keyboard. The keyboard has all standard ASCII key except 96 and 123 though 127 (_, {, |, }, ~, del, ], \). For the longest time I felt the TRS-80 had a black eye because it didn't come with a control key. Well, that's not totally true, there's noe "CTRL" key but there is a control... it's the down arrow key shifted! I don't know how many years I had one of these computers and didn't even know that!! (Though it fairness, it was a Level I system that didn't come with any software, so I didn't use it). So, after learning this, I decided it was time for a list of exactly what all the keys are: Down Arrow - line feed, Up arrow - [, Right Arrow - Tab, Left Arrow - Backspace, Shift + Down Arrow - CTRL, Shift + Up Arrow, ESC, Shift + Left Arrow - CH24, Shift + Right Arrow - CH25, Shift + 0 - Space, Shift @ - `. I should also note that much of my confusion comes from the Color Computer. Both the CoCo 1 and 2 use the exact same key layout as the Model I does, but for whatever reason, Tandy decided to map the keys totally differently! The CoCo does not have a Control key as found on the Model I.
Video: The TRS80 uses a composite video system, capable of 64x16 text resolution. There is no graphics mode on the TRS80, but there are characters that are divided into six sections that can be used to make a 128x48 "graphics" mode as well as boxes and borders. The TRS80 Model III has the same video modes but uses a higher resolution built in monitor instead of a composite monitor. The TRS80 Model IV is capable of both a TRS80 Model III compatible mode, as well as a 80x24 text mode and a true graphics mode. There are optional graphics boards for both the Model III and IV, but I know little about them. The Model II series also offers 80x24 text but I know little more than that. They unfortunatly seem to be lacking the "graphics" charater set, at least one that uses the same charater codes.
Storage: The original TRS80 has both a jack for a standard cassette recorder, as well as an optional floppy disk system that uses the expansion box. Note that the original TRS80 came with a Level I BASIC ROM which will not work with a disk based system. The ROM must be replaced with a Level II ROM in order to use a disk controller. The floppy controller uses industry standard drives, so any low density drive will work with the TRS80 floppy controller. I have been told, though, that Tandy for some reason used the side select line as a drive select, so double-sided drives may require a special cable to work correctlly. The TRS80 Model I originally came with a single density controller, but later double density controllers were offered as well. The TRS80 Model III also has a cassette interface and optional floppy controller. The Model III controller was originally double density. The same floppy system was offered for the Model IV as well. The Model II series uses 8" drives, though high density 5.25" drive will work with with a special cable. This unfortunatly makes it tough to transfer data between different models.
Getting Started: As mentioned above, there seem to be about a million "wiki" type sites on the TRS-80. They tell you what year they came out and how many were sold... but for the longest time I had no idea how to use the think! Just as a little background on me, I started out with a Model I Level I machine, which basically served as a doorstop because the basic doesn't allow "peek" or "poke"s and the cassette baud rate is slower than a level II machine. The best solution I found for that machine was to buy Level I software on cassette. I later ended up with a Level II model I as well as a Model II, Model III, and a Model 4! On the Level II machine, it came with some software on cassette, but I wasn't having any luck loading it. Most computers of the era used CLOAD or CLOADM to load machine language software from cassette. The TRS-80 is a little different (and nicer if you ask me), to load a machine language program from tape, first type "SYSTEM" (without the quotes), this takes you out of BASIC and puts you in a very simple operating system with a *? prompt. To load a program from tape, just type the program name followed by a return, and it will start to load. If all goes well, you'll see two *s on the top right of the screen, the second toggles as data chunks are loaded. Some programs seem to load automaticly, if that doesn't happen, a "/" will run the program. It looks like a "/" followed by a memory address in decimal will jump execution to that location. I'm hoping I can make some cassette images in .wav format to stick on the 'net, as I don't see much out there for download.