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 Post subject: ASCII Video Terminal
PostPosted: Wed Sep 17, 2014 12:54 pm 
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Joined: Wed May 20, 2009 1:06 pm
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Ascii Video Terminal:
http://geoffg.net/terminal.html

ASCII Video Terminal – PIC32MX250
http://micromite.org/shop/add-on-gadget ... ic32mx250/


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 Post subject: Re: ASCII Video Terminal
PostPosted: Wed Sep 17, 2014 7:27 pm 
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ChuckT wrote:

Interesting project. It seems to have the same capabilities as the SECONS µVGA unit, but with greater hardware flexibility, lower overall cost, and access to the µcontroller's software. I like the idea that the unit could be readily integrated into a homebrew 65xx project, since the hobbyist can position components as needed on the PCB.

I'm curious as to what the display looks like on a VGA monitor.

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 Post subject: Re: ASCII Video Terminal
PostPosted: Wed Sep 17, 2014 7:30 pm 
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I think it is a spin off of the Maximite which has eight colors. It is the chip that can do this. I think anyone can reprogram it.

http://geoffg.net/maximite.html


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 Post subject: Re: ASCII Video Terminal
PostPosted: Wed Sep 17, 2014 7:57 pm 
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The SECONS µVGA unit has more pixels but the ASCII Terminal is probably more flexible and cheaper letting the user do more of what he / she wants to do.


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 Post subject: Re: ASCII Video Terminal
PostPosted: Wed Sep 17, 2014 9:15 pm 
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ChuckT wrote:
The SECONS µVGA unit has more pixels but the ASCII Terminal is probably more flexible and cheaper letting the user do more of what he / she wants to do.

More pixels, at least in the case of the µVGA, doesn't translate into a better display. The widely used WYSE 60 terminal has a lower display resolution than that of the µVGA (the 60's design dates to the mid-1980s), but has as good an appearance.

The flexibility of Geoff Graham's design is what got my attention, especially since it's built from a pile of readily-available parts. Also, the VT-100 implementation looks to be more complete in most respects than µVGA's. As the source code for the PIC is available, one could add features, assuming the PIC has enough memory to hold the expanded code. For example, this design doesn't support multiple text colors—color has to be selected via jumpers on the PCB. I suppose one could modify the design to individually drive the color signals, complemented by extra code to support ANSI escape sequences for changing color.

I may consider building one of these after I get POC V2 up and running, as it seems to be a relatively easy thing to put together (it could be built on perf board). V2's console port can be jumper-set to be a true TIA-232 port or a TTL serial port. The latter setup was concocted to allow me to use my µVGA module as a console, along with a PC keyboard and VGA monitor. The TTL setup, with a minor modification, should work equally well with Graham's design.

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I think it is a spin off of the Maximite which has eight colors. It is the chip that can do this. I think anyone can reprogram it.

The core of the whole design is the code that Graham wrote to run in the PIC controller. He originally published it in the Maximite project.

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 Post subject: Re: ASCII Video Terminal
PostPosted: Wed Sep 17, 2014 11:16 pm 
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The screen resolution for the video terminal seems to change depending on the mode. The source suggests its 80x36 (characters) in VGA, 50x18 in PAL composite, 50x15 in NTSC composite.

The picture is generated by DMA transferring monochrome pixel data to an SPI channel. Adding colour could be hard. You would need to increase the size of the buffer required to hold the image data, possibly exceeding the available RAM. Whilst there are lots of DMA channels I think only one is active at a time so to synchronize three colour pin outputs you would need to DMA the image on a single channel wasting 5 of the bits in each byte and lots of memory. So I think colour is out unless you use a TQFP chip with lots more RAM.

The SECONS uVGA uses a lower spec CPU (a dsPIC) in conjunction with a CPLD to generate its colour outputs. It must be generating the image for a row of one character while the CPU is fetching the data for the next.

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 Post subject: Re: ASCII Video Terminal
PostPosted: Tue Sep 23, 2014 4:31 pm 
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BigDumbDinosaur wrote:
The flexibility of Geoff Graham's design is what got my attention...

The Australian publication Silicon Chip makes the ASCII terminal PIC available with the firmware loaded and ready for use. I decided to order one—it came to about 21 dollars US, including shipping. Yes, I could buy the PIC for about a third of that, but I don't have a PIC programmer. So the Silicon Chip offer is a good deal for a one-off build.

Speaking of a one-off build, the terminal circuit is simple enough that it can be assembled on a piece of perf board. The trickiest part of the build will be probably be soldering connections to the keyboard and VGA receptacles.

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 Post subject: Re: ASCII Video Terminal
PostPosted: Wed Jan 14, 2015 3:30 pm 
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Joined: Sat Dec 08, 2012 8:29 pm
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great thinks, thank you for the link =)


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