TRS-80 Model III UART serial card alternative

Discussion in 'The Projects Forum' started by programmer6502, Feb 1, 2014.

  1. programmer6502

    Thread Starter Member

    Feb 1, 2014
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    Hello! I got a fun project for you guys ;)


    I have a TRS-80 Model III and if you guys remember TRS-80’s, some had RS232 serial communication cards with UARTs. Unfortunately, my TRS-80 is a base model so it has no RS332 serial communication card. I would like to add one for convenience in file transfer since floppy’s are getting more and more obsolete. I understand I could find the original Radio Shack RS232 card on ebay but at this moment they’re pretty expensive. So what I want to do is either make my own or modify an old say, PC UART card. (Plus who knows if the originals still work most of the time)

    I was debating on whether to build my own when a friend gave me an old PC serial communication card. I would like to try and modify it to work if possible. It’s a Mouse Systems Corp 301035-001 REV C UART card. I looked it up and didn’t find much information about it.

    (I couldn’t fit all my information and photo’s on here so please visit the link to my blog and read the latest post)
    Blog post link

    Assuming you read the blog post, here are my questions. I need help figuring out how to connect this safely to my TRS-80. I assume I can just hook up the data lines the way they are, connect the clock output line to the clock section of the PC UART board, and hook up both resets the way they are as well. If all is correct there, then that leaves me with the interrupt lines, the address lines, and the RS232 I/O lines on the TRS-80 end. Then I could just pull up/down the unneeded pins with resistors.

    Sorry it's really messy,
    Any help would be greatly appreciated!


    Note: due to size limits I cannot attach the TRS-80 III service manual but it can be found here if needed: model iii service manual (1980)(radio shack)(pdf).zip
     
  2. takao21203

    Distinguished Member

    Apr 28, 2012
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    I have some old Z80 SIO chips available.

    Using a PC card with Z80 will be difficult, and unusual.

    do you have the schematic for the original RS232 card?
     
  3. programmer6502

    Thread Starter Member

    Feb 1, 2014
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    Yes. It along with other information is available in the service manual I mentioned on the bottom of my last post. There should be a download link.
     
  4. programmer6502

    Thread Starter Member

    Feb 1, 2014
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    This is pretty helpful too:rs-232-c (1978)(tandy)(pdf).zip. This manual is for the original TRS-80 RS232 interface for the model I. This interface is pretty much the same as the model III's controller except this one doesn't support interrupts.

    What are the chip numbers on those Z80 SIO chips you mentioned?
     
  5. spinnaker

    AAC Fanatic!

    Oct 29, 2009
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    It is a zip file. Lots of people won't open it. Can you post in a pdf?


    Eons ago, I built an rs232 interface for my Atari 800. Since the Atari already had serial i/o, all I had to use was some rs232 level shifting chips.

    The Atari serial I/O used a smart multi-drop system were each device would report on the bus. I did not want to get into all of that so I wrote my own device driver and talked direct to the RS232 port.

    Unless you can duplicate the TRS80 RS232 interface pretty closely, you might have some coding to do to.
     
  6. spinnaker

    AAC Fanatic!

    Oct 29, 2009
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    What kind of interface did the floppy drive use? Maybe you could build an interface between the old floppy cable and a thumb drive?

    You could also build a SD memory interface between the parallel port and or serial port.

    But you would still need a way to load the software to handle it.

    The floppy conversion seems the most promising but also the most challenging.
     
  7. takao21203

    Distinguished Member

    Apr 28, 2012
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    after looking at the schematic there is not much hope to use a PC card, also no z80 SIO chip here.
     
  8. programmer6502

    Thread Starter Member

    Feb 1, 2014
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    Thanks, I didn't know that. I don't have a way uploading my own files (I would do it on here but the upload size max is too small.) But I found a PDF version of the TRS-80 service manual here. Unfortunately I can't find a non-zipped version of the model I RS232 interface PDF.

    That's awesome! I have a few Atari's myself.
     
  9. programmer6502

    Thread Starter Member

    Feb 1, 2014
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    So is there anything I can do besides get an original controller? I wounder if they have any newer UART chips I could use. I've looked at some more modern UART's on Jameco.com and a lot of them have most functions of the original circuit in one chip.
     
  10. programmer6502

    Thread Starter Member

    Feb 1, 2014
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    I can only upload one because the other is bigger then the max 5MB upload size. Here's the model I interface manual.
     
  11. JohnInTX

    Moderator

    Jun 26, 2012
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    The TRS80 III used a TR1602A (AY-3-1015) UART on the native TRS80 bus. The board you have uses the much later NS16450 on an ISA bus. There are many differences in the chips and busses. The TRS manual describes the bus signals. Compare the signals and timing with ISA. I think you have some logic to do.

    The 1602 is a very simple UART that just transmits what's on its pins when you strobe it. The receiver is simple as well. The 16540 is register based which would require new drivers (which require rebuilding CP/M? or patching TRSDOS, IIRC) just to configure it.

    Its doable in concept but it won't be trivial.

    Attached is some info I dug up so you can compare the two UARTS.

    Have fun!
    eBay listing for TRS80 III SIO

    Datasheets for the two UARTS are attached.
     
    Last edited: Feb 2, 2014
  12. programmer6502

    Thread Starter Member

    Feb 1, 2014
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    Thanks! I really appreciate it!
     
  13. t06afre

    AAC Fanatic!

    May 11, 2009
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    Since the uart is quite simple. Maybe you can program some micro controller to emulate the tr1602a uart
     
  14. spinnaker

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    Oct 29, 2009
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    That was my thinking. A Max1232 and your good to go except for the address bus issue. I would think the interface would need to appear in the same address space as a normal rs232 interface card.
     
  15. programmer6502

    Thread Starter Member

    Feb 1, 2014
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    That is a great idea! I don't have any experience with microcontrollers though. But I know they're pretty simple.

    For another alternative, I found this very simple Kaypro II SIO controller. It looks like it will work. I don't know if the 3884 UART is still available though, maybe there's something similar. This controller has two address lines and the same clock speed as the TRS-80. The Kaypro is a Z80 machine as well. But yeah, a microcontroller would be even better!

    [​IMG]
     
    Last edited: Feb 2, 2014
  16. programmer6502

    Thread Starter Member

    Feb 1, 2014
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    Okay, I think this is actually a Z8440. I found a couple and they're pretty cheap.
     
  17. t06afre

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  18. programmer6502

    Thread Starter Member

    Feb 1, 2014
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    Yeah I was debating on that too. Of course the original TRS-80 had 5.25" drives but there's a cable that can be built to use 3.5" drives. Since 3.5" drives have the IDE connection, that makes it so I could probably connect an IDE device like that to the TRS-80.

    Here's a PDF about the capacity of the floppy drive and how to install 3.5" drives. It looks like the FDC capacity is 40 or 80 tracks, and single or double density. In the PDF I attached, the author uses a standard IBM style 3.5" drive. So I would assume it's a 1.44MB drive. So that would work.

    Now that I think about it and because of my lack of experience, this might be a better and simpler way to go. That would be awesome having a USB port too! It would defiantly be faster then RS232 serial transfer.
     
    Last edited: Feb 3, 2014
  19. takao21203

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    Apr 28, 2012
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    why do you want to use this old machine? For nostalgic reasons? One 3 dollar microcontroller from today is 10x as powerful as all the circuits from the z80 design all together.

    You can add USB very easily if you can program a software for it yourself, all you need is a USB/TTL converter, and then you need a microcontroller. If it has enough pins it can do all the address decoding for the z80 bus.

    You are better off (for spending your time) reading a microcontroller manual.

    Try the 16F with 44 or 64 pins, they are more easy than 18f or PIC32.

    Or maybe an Arduino can do it.

    Remind the serial port won't work in the z80 system DOS, you need to write software for this yourself. Is this machine programmed in assembler? Do you have one on the system or do you use a cross assembler maybe? Or BASIC?

    All you need is really a PIC controller which only costs a few dollar.

    The original system had 9600 baud and that is very slow for nowadays standards.

    Emulating the original bus protocol with a microcontroller looks like way too much effort to me. But if you look the links, such products do exist for floppy drives.

    Maybe i have a few of these around somewhere, eventually even on adapter board: http://www.microchip.com/wwwproducts/Devices.aspx?dDocName=en023674

    But the big question is really why you need to work with this old stuff? Just for entertainment?

    I tried some years ago with home computers again but quickly abandoned it- some parts did not work right, and costs spiralled out of control.

    Remember most of these early computers were kind of a vapourware- they were not really fit for the purposes shown in the adverts, and within a few years, they all disappeared again.
     
  20. programmer6502

    Thread Starter Member

    Feb 1, 2014
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    You do have a point, this has crossed my mind many times. The truth is, I don't know why I like vintage computers. I wasn't even born in their time. Part of it started for collectors reasons, (as they are worth more and more as time goes on) but I thought there's really no point in having them just to do nothing with them. My first computer was an Atari 800XL. They told me I was only going to like until I realized it does nothing. But that wasn't that case. I ended up spending a year or two learning Basic with it. That's pretty much how it started. It's a really long story. I've just had a fascination for them. But yes they can be a huge pain but you can learn so much with them and believe it or not, a lot of that knowledge has come in really handy for me with new technology too.

    I'm very aware of the stuff you mentioned and I'm interested in that too. It's amazing what you can do and get now days and for how cheap! I actually have many upcoming projects with microcontrollers but one thing at a time. (Not to mention I recently completed a new top of the line desktop) You're also right here, vintage tech project prices do get ridiculously expensive but most of the time I think it's worth it. I enjoy it and again, learn so much.

    And yes to program that for the TRS-80 I would use assembly for the RS232. There's a manual explaining how to do that. Also, 9600 baud is pretty fast on a TRS-80, you can't really compare that with new computers. (The model III I have can actually support 19,200 baud) And also, just so you know, the TRS-80 model III has built in Basic.

    Time will tell but I do plan on getting into the kind of stuff you suggested. I also think combining old with new is pretty cool.

    So anyway
     
    Last edited: Feb 3, 2014
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