Electronics > Projects, Designs, and Technical Stuff

Cloning a Tandy TRS-80 Model 1

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GK:
Well, here is a video. Powering on, checking the free memory and then loading Radio Shack Flying Saucers via the cassette interface from my crappy Digitech digital audio recorder. Quite possibly the very first TRS-80 ever up and running on breadboard  :)


http://youtu.be/dClOHNcpnVw

MustardMan:
That is certainly one hella rats nest you have there!

I do have one level 1 cassette in my collection (a real one from Tandy!). Chess. According to "WAV2CAS" it has decodable Level 1 content on the tape. A couple of recognised SYSTEM files (with a valid checksum), and some other stuff that appears OK with recognisable ASCII in it, but WAV2CAS says it is bad. I never played/ran it because I had a L2 machine, and the L2 version was on the reverse side of the tape. I can send you a WAV (or compressed in some format), but as far as I know the game has no sound - which is one of the things you wanted. I could send a CAS, but that would be assuming that WAV2CAS got the decode right, and from my experience, that is not always the case.

Edit: By the way, what sort of keyboard interface did you decide to go with?

GK:
Oh that's OK, I just went ahead and did the video without sound effects so it doesn't matter anymore. The next video will be of the completed machine running Level II Basic and probably some derivative of Space Invaders....to continue with the theme started with my PET clone. I have a *.cas file of "Micro-Chess" for 250 baud, which might be the same Chess game you've got (from here: http://www.classiccmp.org/cpmarchives/trs80/mirrors/pilot.ucdavis.edu/davidk/trs80/software/cassette.htm ). I still have the PIC+EPROM on the breadboard for interfacing the keyboard. I've designed the proper interface with an MAX 7000 CPLD.

GK:
I've had a cool idea for another home brew computer peripheral - a PS/2 interface/converter for a standard Atari joystick port. I'm thinking a PIC micro interfaced to a bunch of buttons and a standard 2x16 LCD display for the user interface.

With the Atari port you have 5 discrete switch/sense inputs:

1) Fire
2) Up
3) Down
4) left
5) Right

.....plus four additional states (combinations):

6) up+right
7) down+right
8) down+left
9) up+left


My idea is that you can scroll through these nine switch states and assign to each any possible PS/2 key character make/break code to be sent when true/false. A complete set can then be saved as a unique preset (with an x-digit name that you can enter for easy identification later). Lets say I choose a PIC micro with enough internal EEPROM memory to store 100 "presets". Maybe (actually definitely) add auto-repeat as a selectable enabled/disabled option for each state with a programmable repetition rate.

Now you can play all of your retro 8-bit keyboard games with a joystick, provided that you have already upgraded your vintage machine or clone with a PS/2 keyboard interface. Such a device might also appeal to enthusiasts of vintage PCs which use the PS/2 protocol natively. Maybe add AT functionality as well? 

The thing could be built into a not very large box with PS/2 in/out through ports and perhaps even auto-switching so that you can just plug everything in and not have to swap out your keyboard every time you want to use the joystick.

Thoughts?

kizmit99:
I think it's an interesting idea...  certainly (on the surface) seems like a doable approach.

I would think you'd pretty-much *have* to be able to use both the keyboard and the joystick at the same time though.  Otherwise I suspect most games wouldn't be playable.  I know I die quick enough that I'm having to choose "one or two player mode" quite often  :-DD (and that usually involves typing keyboard keys).  Others may have issues when it's time for them to enter their initials for the high-score page...  :)
I know for the PS/2 keyboards I've looked at closely, neither of them required any kind of setup from the host to get them talking, but I feel like I've read  somewhere that some do  :-//   With that, using the PIC to merge the two PS/2 streams shouldn't be difficult.

To be honest though - while an interesting exercise I probably wouldn't use one.  Part of the 'thrill' of the retro machines is their sometimes awkward primitiveness...

Just my thoughts...

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