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Forum Index : Microcontroller and PC projects : TRS-80 Model I level II
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MicroBlocks Guru  Joined: 12/05/2012 Location: ThailandPosts: 2209 |
I made the decision to rebuild one of my favorite computers. The TRS-80 Model I level II, with some modifications of course to be able to use current screens, easier with static rams instead of the dynamic ones, etc. Functionality it should of course stay the same. So no more emulation! Unfortunately i have lost my large amount of manuals and documentation when i emigrated. Especially the ones that have the complete schematics and the complete Level 2 roms disassembled with comments for every routine in there. I saw that a few members had this computer before and i would like to request if someone can make a copy of it. Most important are the schematics (i remember it was a foldout of about 4 pages!) because i want it to be functionally exactly the same, especially keyboard and screen mappings as a lot of software especially games were written in assembler and used the direct access to those. Any info that helps me build this thing is very welcome! Edit: Well, that is special! After looking again i found this: http://www.1000bit.it/support/manuali/manuali.asp A great resource! Microblocks. Build with logic. |
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donmck Guru Joined: 09/06/2011 Location: AustraliaPosts: 1313 |
Noble task, but I think a massive task as well. In short, mostly LS technology, you will have trouble getting the 2102 chips, but static is fine. You should be able to chase the rest. If I wanted to do it, I would be buying an old unit that I could either fire up, or repair, in order to fire up. That would save a few hundred hours I am sure. An alternative is to use a MaxiMite-DuinoMite with Ken Seglers TRS-80 Emulator: 
If you can handle C, then you can have it all running without too many tears. Plenty of I/O, SD drive, UARTs, etc. Cheers Don... https://www.dontronics.com |
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| MicroBlocks Guru Joined: 12/05/2012 Location: ThailandPosts: 2209 |
Yeah, but that is already done so many times. I want no emulation. The challenge is the hardware, emulating a Z80 is not enough. :) The way i think about it now is to use current versions of RAM/ROM as prices of larger memories are no problem anymore. :) I can leave out the refresh part altogether. Using a 32k/64k static ram and a 32k/64k eprom i can get rid of a difficult memory part without changing its function. Power supply would be easy, Keyboard is just a matrix so that would not be difficult. More than one key at the same time is the only way to get old games to play right. Video the original way would be difficult, i could try to emulate a MCM6670P with a small mcu, or think of something easier. According to Motorola's datasheet the way to get a character set programmed into the chip would be to supply a Hexadecimal coding using IBM Punch cards or a Hexadecimal coding using ASCII paper Type Punch. I guees that way is closed. :) Tape and relay, easy. Then of course put it on some circuit board that will be easily extendable, the Z80 has a great way to use I/O. 256 ports and when using the upper 8 address bits even 65536 ports. That would be a possible 524288 GPIO pins. :) :) I am currently thinking of some type of motherboard with 50 pin connectors and a few small modules like power supply, cpu+buffer chips, RAM/ROM, video/keyboard and then be able to make specific io boards all controllable with Z80 assembler. :) DMA/CTC/SIO/PIO are all still easily available and those even have interrupt and DMA support. Still have to find/buy a level II rom set as my hex dump is somewhere in bit heaven. Programming it in Basic would be nice for the kids (and for me :) ). So i guess it will be ready somewhere next year. :) Microblocks. Build with logic. |
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Nick Guru Joined: 09/06/2011 Location: AustraliaPosts: 512 |
Maybe do the video in a small easy to obtain and microcontroller chip but still use a real Z-80? |
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| MicroBlocks Guru Joined: 12/05/2012 Location: ThailandPosts: 2209 |
I have the specs of the MCM6670P chip and a sample character set, finding out which characters were in use by the TRS-80 i should be able to find somewhere. It is just a rom with som extra logic that spits out bits so it should not be difficult to make with a pic. Now still have to find my assembler/disassembler/in circuit debugger i made many years ago. Microblocks. Build with logic. |
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| Nick Guru Joined: 09/06/2011 Location: AustraliaPosts: 512 |
Wow. I'm amazed by your determination! I too was a TRS-80 Model 1 buff having spent many hours programming Z-80 assembly language games for it in the early 80's. Unfortunately, I never got rich from it but I did create some great games. I loved that machine! 
The Maximite TRS-80 firmware does a mighty fine job of converting the Maximite into a TRS-80. It just needed to be completed. If you know C programming, you could look at taking over from this. I can understand why you like the challenge to build one from scratch... if you have the free time. Nowadays, everything can be just programmed into a microcontroller with minimal hardware. I fully understand your motivation and I applaud you for that. Nick |
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| mookster1 Regular Member  Joined: 10/06/2011 Location: New ZealandPosts: 81 |
Found a place with some manuals for your TRS80... http://www.1000bit.it/scheda.asp?id=110 I found the service manual for my TRS80 Model 4P on here. There's a LOT of really useful stuff here if you dig around
EDIT: Damn it, I didn't read the edit at the bottom of your post! Oh well...  Capacitance is futile - roll on 2012! |
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| MicroBlocks Guru Joined: 12/05/2012 Location: ThailandPosts: 2209 |
The model 4p was the computer that cost me a lot of work as i had to earn the money for it over a long time. I even had it expanded with a graphics card and slimline double sided high density floppy disk drives. Worth every cent though. :) As it was together with the model 1 the start of a career. I remember writing a KSM program to have programmable macros and a few other things like a voice synthesizer and of course a BBS. :) I had 2 modems and the 4p was the host. I needed special modems because in those days most people had 1200/75 baud modems used for viditel. So i had to have 1200 baud sending and 75 receiving. That was at that time very difficult but with lots of help from a few people from the local computer club got it working. The reason for a trs-80 model 1 clone is to give my kids at least the same basic knowledge about computers so they don't end up as only a user that have no idea what makes a computer work. And what better than with a computer that not only exists of large flat pieces of plastics. :) And of course give me a challenge to exercise my brain and memory. Thinking about the project more i feel i only have real trouble with getting the video to work on a vga monitor. I want to use the character generator and video memory as in the model 1 and adapt that to have the right signals. Need to study more about vga timings, i know all about resolutions but that part i never had the need to make myself before. Analog, brr... :):) Microblocks. Build with logic. |
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bigmik Guru Joined: 20/06/2011 Location: AustraliaPosts: 2914 |
Damn TZ, About 18 months ago I chucked out all my Z80 `junk' including my all time favorite a full page plasticised 1 page circuit schematic of the TRS-80 about 1000mm by 800mm in size... it was my bible... I bought it from BYTE magazine from Steve Ciacia (circuit Cellar) ... they may even still have some... I tossed out `programming the Z80 by Rodnay Zacs' amongst other books... I have a CD that is compiled and sold by an old colleague of mine for around $15 that might be of interest to you... I cant locate his contact details but the web site on the front cover is TRS-80 and this is the readme file on the disk 2012-06-06_232934_readme.zip PM me if this is of great interest and I will try hgarder to dig out his contact details for you Regards, Mick Mick's uMite Stuff can be found >>> HERE (Kindly hosted by Dontronics) <<< |
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| MicroBlocks Guru Joined: 12/05/2012 Location: ThailandPosts: 2209 |
I still have the Rodnay Zaks book, if it is the one with a split earth and a lightning bolt. "Programming the Z80". It is still complete although the pages are have signs of use. :) I found a complete schematic, and it is the one i remembered on the link i have in the first post. (Technical reference for the model I pdf) I will look at that site and readme. Thanks for that! Microblocks. Build with logic. |
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djuqa Guru Joined: 23/11/2011 Location: AustraliaPosts: 447 |
If I was revisiting the Z80 Based TRS80, the processor to be chosen now would be either the eZ80 50mhz chip or something like the PIC32 emulating the z80. Ram handled by any of several cheap Serial SRAM chips & ROM/Floppy Disk/H-Disk easily handled/emulated by SD card. Video generated by FPGA or 1 of several cheap dedicated MCU's capable of generating VGA/HDMI signals. Keyboard would be no problem. So would I do it. NO WAY, Jose I would look at the pictures of my old 1978 Model 1 16K TRS-80 (One of the first in Aussie) for about 10 minutes. Then come to my senses and be thankful the last 30+ years has bought in computing. If you really want your kids to learn about computing get them a Duinomite / Maximite of their own. Install the TRS80 Emulator for a bit of a giggle. But trying to relive the "Gold Old Days" by trying to resurrect the crudely designed and manufactured TRS80 is a folly that will only turn into a money pit. VK4MU MicroController Units |
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| donmck Guru Joined: 09/06/2011 Location: AustraliaPosts: 1313 |
ME2 What David said
Don... https://www.dontronics.com |
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| Nick Guru Joined: 09/06/2011 Location: AustraliaPosts: 512 |
If you made it small and cost effective, maybe you can offer it to Radio Shack in the US to sell in their stores as a kit or ready made. Or to Dick Smith (if they don't go broke) as a System 80. A retro computer kit available in a large scale retail outlet for the Geek masses or as an educational kit used in a high school computer subject. What a great idea eh? (And the tooth fairy IS real!) 
Nick |
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| MicroBlocks Guru Joined: 12/05/2012 Location: ThailandPosts: 2209 |
:) The nice thing about little projects like this is that they don't have to make sense at all! :) My desk is full of mcu's of every kind, from pic(axes) to avr's, never liked fpga's. I like the maximite because of its vga, even if it looks crude on an lcd, and soon even in color! As a small computer the maximite also not really makes sense, everything it does can be done much more efficient in another way. But somehow it is just so versatile and very quick and easy to build something that controls things even as simple as a led. Making that blink i can buy a 555 and some R and C maybe even a potentiometer to control the rate of blinking. Is that fun, it was when i was starting to learn, and it was fun again when i used a PIC to do the same and fun again when i used a ARM Cortex-M3. :) The Z80 btw is the most successful cpu ever, that it is still being made is the proof. So instead of using a 20MHZ or even a full blown PC to emulate it (what is the usecase there?), use the real thing at 8Mhz. :) Anyone remember a Micro-Professor? That was a fun thing too. Microblocks. Build with logic. |
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| donmck Guru Joined: 09/06/2011 Location: AustraliaPosts: 1313 |
Level II ROMs are 1978, which is 34 years. Just wondering what the legalities would be on distributing copies of these. Don... https://www.dontronics.com |
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| MicroBlocks Guru Joined: 12/05/2012 Location: ThailandPosts: 2209 |
I think they are still not public domain. TRS-80 simulaters don't distribute the rom image with it, but it still can be found, (i found one yesterday). I guess MS still has the rights. Microblocks. Build with logic. |
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| Nick Guru Joined: 09/06/2011 Location: AustraliaPosts: 512 |
Seriously, why not design it as an easy to construct kit. Keep it simple and document the assembly and theory of operation so that a high school kid could learn about computers. The Maximite is much like that but the PIC32 is beyond most people's soldering abilities and keep the port count low to make it easy to build. (Add an expansion connector to a more advanced I/O board later for the next advanced level of the kit). You could design a complete computer class curriculum based on this kit. There's potential there, for anyone who has the drive. Nick |
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| MicroBlocks Guru Joined: 12/05/2012 Location: ThailandPosts: 2209 |
A z80 learning tool i used a lot was the Microprofessor. Very easy to experiment with. Single stepping, register inspection was all possible and made debugging a lot easier. I remember connecting a 2 lines lcd to it and changed the monitor program to have all the registers displayed on it while single stepping or on a breakpoint. I used it for prototyping many projects. For learning how things work starting from the basics and working your way up, you can't get any better than that i think. Maybe time for a modular system that recreates that. Microblocks. Build with logic. |
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vasi Guru Joined: 23/03/2007 Location: RomaniaPosts: 1697 |
I still have a Z80 in my box (along with PIO80 and 8255, I guess...). In which way is better than ATmega644P/1284P or lets say, PIC18F46K22 if is about blinking a LED, interfacing it with various sensors and peripherals? A good Z80 assembler on Linux is pasmo which can be used with an IDE (zDevStudio) written in Lazarus and Freepascal. Both the IDE and assembler are cross-platform. Hobbit name: Togo Toadfoot of Frogmorton Elvish name: Mablung Miriel Beyound Arduino Lang |
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| MicroBlocks Guru Joined: 12/05/2012 Location: ThailandPosts: 2209 |
Assembly language for one thing, it has clear separation between registers, memory, output ports, etc. For everything you want to connect you need a cheap chip. More is done in hardware than software, that is an advantage in a lot of cases! The biggest advantage though is to be able to complete grasp it, both in hardware characteristics and software. The reason is that unlike many mcu's that go through very quick enhancements and even are completely replaced making new designs necessary, the z80 is still the same after 36 years! For learning, you actually have to learn something about gates, latches, counters, dividers etc like the 74LS series instead of taking over those functions in software. With that knowledge you would be able to switch something in a few nanoseconds and solve things like flip/flops, buffering, etc,etc in hardware alone. Try having 24 LEDs on for a while, i bet the mcu gets a little too hot, with just a few 74LSxx's that is no problem, and when you did something wrong probably only that 74LSxx was broken. Beginners not really watch max power sourcing or sinking per gpio and certainly not combined. And for that matter some more experienced make that mistake too sometimes. So for learning and then using hardware a 'bare bones' processor is better that an all in one mcu. For software, i think there is not a bigger library of software than for the Z80, and you can try and debug it on one of the many simulators to test your software without needing hardware. As a product, i guess the people who are getting older and are going to have a lot of free time for a hobby would prefer it because there is a big chance that those old guys grew up with it. :) For myself, i think i am a very practical and cost aware person. If i need to make something very simple i take a picaxe, is it more complicated then i use a pic or a Z80 and program it in C with MLab or assembly, if need more power which happens seldom than i can choose the ARM's or sometimes a propeller (parallel heaven and hell :) ), no still not like fpga's :). Every project big and small has its best match in one of those choices, and actually a lot more than a few were done with a simple Z80 as its controlling heart. Microblocks. Build with logic. |
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