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Re: Text video driver

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Re: Text video driver by Unknown on Aug 7, 2006			Not available!
look at the displaytest project on www.fpgaarcade.com for spartan3e kit. it also has instructions for a 12bit colour mod. It does not contain the text roms, but it used to :) Cheers, MikeJ. Lauro, John writes: [q] Just purchased and received a Xilinx Spartan-3E starter kit. Trying to teach myself from all the information available on the web... It's the fastest or densest FPGA board, but seems to be the best starter board for the ~$150 price range I found with a decent (500+K gate equiv) and a reasonable amount of on board interfaces (including 10/100 Ethernet phy) to test with.... I did find the full VGA cores on the opencores site. I am wondering if anyone has a text based video core they could point me to. (If it matched the 8 color (3 bit) of the starter kit that would be ideal). I want to keep the resources for video to a minimum, but I do want to provide a console and/or status display. If not, I'll try to create one and make it available for everyone to critique... (If I do it, it will probably not be pretty... software guy trying to do hardware logic for the first time...) If anyone has any pointers to reference designs or sample projects of any kind that will easily work with this board, let me know. (Especially if they use either the Ethernet or video ports. [/q] look at the displaytest project on www.fpgaarcade.com for spartan3e kit. it also has instructions for a 12bit colour mod. It does not contain the text roms, but it used to :) Cheers, MikeJ. Lauro, John writes: Just purchased and received a Xilinx Spartan-3E starter kit. Trying to teach myself from all the information available on the web... It's the fastest or densest FPGA board, but seems to be the best starter board for the ~$150 price range I found with a decent (500+K gate equiv) and a reasonable amount of on board interfaces (including 10/100 Ethernet phy) to test with.... I did find the full VGA cores on the opencores site. I am wondering if anyone has a text based video core they could point me to. (If it matched the 8 color (3 bit) of the starter kit that would be ideal). I want to keep the resources for video to a minimum, but I do want to provide a console and/or status display. If not, I'll try to create one and make it available for everyone to critique... (If I do it, it will probably not be pretty... software guy trying to do hardware logic for the first time...) If anyone has any pointers to reference designs or sample projects of any kind that will easily work with this board, let me know. (Especially if they use either the Ethernet or video ports.

Re: Text video driver by Unknown on Aug 7, 2006			Not available!
Hi Mike, One suggestion I heard, if you do not want to modify the board, is to pulse width modulate the VGA signals. I have not tried it myself, but if you can get a DCM running at 75MHz you should be able generate a 3 bit PWM code on each VGA bit using a 25MHz pixel clock. This will will give you 4 intensities per bit (including black) or 64 colors in total. It's not great but better than 8 colours. My concern with using the FX2 connector is that I want to use the digilent VDEC-1 Digitizer. Seems crazy to have the color digitizer support and not be able to display the output ... but there you go. John. mike johnson wrote: [q] look at the displaytest project on www.fpgaarcade.com for spartan3e kit. it also has instructions for a 12bit colour mod. It does not contain the text roms, but it used to :) Cheers, MikeJ.[/q] -- <A HREF="http://members.optushome.com.au/jekent">http://members.optushome.com.au/jekent</A> Hi Mike, One suggestion I heard, if you do not want to modify the board, is to pulse width modulate the VGA signals. I have not tried it myself, but if you can get a DCM running at 75MHz you should be able generate a 3 bit PWM code on each VGA bit using a 25MHz pixel clock. This will will give you 4 intensities per bit (including black) or 64 colors in total. It's not great but better than 8 colours. My concern with using the FX2 connector is that I want to use the digilent VDEC-1 Digitizer. Seems crazy to have the color digitizer support and not be able to display the output ... but there you go. John. mike johnson wrote: look at the displaytest project on www.fpgaarcade.com for spartan3e kit. it also has instructions for a 12bit colour mod. It does not contain the text roms, but it used to :) Cheers, MikeJ. -- http://members.optushome.com.au/jekent

Re: Text video driver by MikeJ on Aug 7, 2006			MikeJ Posts: 10 Joined: Jan 16, 2002 Last seen: Feb 9, 2021
Hi John, I have heard the same, but I was lazy and I knew adding a few resistors would work - and it's less typing :) Cheers, Mike. [q] Hi Mike, One suggestion I heard, if you do not want to modify the board, is to pulse width modulate the VGA signals. I have not tried it myself, but if you can get a DCM running at 75MHz you should be able generate a 3 bit PWM code on each VGA bit using a 25MHz pixel clock. This will will give you 4 intensities per bit (including black) or 64 colors in total. It's not great but better than 8 colours. My concern with using the FX2 connector is that I want to use the digilent VDEC-1 Digitizer. Seems crazy to have the color digitizer support and not be able to display the output ... but there you go. John. [/q] Hi John, I have heard the same, but I was lazy and I knew adding a few resistors would work - and it's less typing :) Cheers, Mike. Hi Mike, One suggestion I heard, if you do not want to modify the board, is to pulse width modulate the VGA signals. I have not tried it myself, but if you can get a DCM running at 75MHz you should be able generate a 3 bit PWM code on each VGA bit using a 25MHz pixel clock. This will will give you 4 intensities per bit (including black) or 64 colors in total. It's not great but better than 8 colours. My concern with using the FX2 connector is that I want to use the digilent VDEC-1 Digitizer. Seems crazy to have the color digitizer support and not be able to display the output ... but there you go. John.

Re: Text video driver by Unknown on Aug 7, 2006			Not available!
John Kent wrote on Tue, 08 Aug 2006 00:46:43 +1000 [q] One suggestion I heard, if you do not want to modify the board, is to pulse width modulate the VGA signals. I have not tried it myself, but if you can get a DCM running at 75MHz you should be able generate a 3 bit PWM code on each VGA bit using a 25MHz pixel clock. This will will give you 4 intensities per bit (including black) or 64 colors in total. It's not great but better than 8 colours.[/q] Wouldn't the PWM clock have to be 8 times the pixel clock instead of just 3 times? Not that 200MHz is such a big deal on a modern FPGA... As for text output, I tried the "XSA 50 terminal program" from <A HREF="http://www.xess.com/ho03000.html">http://www.xess.com/ho03000.html</A> and it worked ok, though having to program the Flash chip with the character patterns is a small complication. In thinking about using blocks RAMs for that instead I came up with the idea of limiting myself to the 96 main ASCII characters and stuffing three (5 bits wide) in each 16 bit word, so a 256 by 16 BRAM (Spartan 2) could include 224 words for 32 groups of 7 line high characters and still have 32 words left over for a state machine to generate all the timing. For a Spartan 3 the 1024 by 18 BRAM would even have room for the text buffer (only enough for 64 by 24, unfortunately). -- Jecel John Kent wrote on Tue, 08 Aug 2006 00:46:43 +1000 One suggestion I heard, if you do not want to modify the board, is to pulse width modulate the VGA signals. I have not tried it myself, but if you can get a DCM running at 75MHz you should be able generate a 3 bit PWM code on each VGA bit using a 25MHz pixel clock. This will will give you 4 intensities per bit (including black) or 64 colors in total. It's not great but better than 8 colours. Wouldn't the PWM clock have to be 8 times the pixel clock instead of just 3 times? Not that 200MHz is such a big deal on a modern FPGA... As for text output, I tried the "XSA 50 terminal program" from http://www.xess.com/ho03000.html and it worked ok, though having to program the Flash chip with the character patterns is a small complication. In thinking about using blocks RAMs for that instead I came up with the idea of limiting myself to the 96 main ASCII characters and stuffing three (5 bits wide) in each 16 bit word, so a 256 by 16 BRAM (Spartan 2) could include 224 words for 32 groups of 7 line high characters and still have 32 words left over for a state machine to generate all the timing. For a Spartan 3 the 1024 by 18 BRAM would even have room for the text buffer (only enough for 64 by 24, unfortunately). -- Jecel

Re: Text video driver by Unknown on Aug 8, 2006			Not available!
Hi Jecel, I don't see why the PWM needs to be 8 bits long. It can be any length you want depending on the clock rate and the resolution required. The problem with PWM is that it is a decoded bit stream, so it's order N+1 (?) ie. doubling the number of bits in the PWM shift register doubles the number of colors but halves the resolution of the display for a given clock rate. I'm not sure how it would look either for long PWM values. You might have to come up with some sort of scheme to dither the pixels in the shift register so you have 101010 instead of 111000 for 50% duty cycle. John. Jecel Assumpcao Jr wrote: [q] John Kent wrote on Tue, 08 Aug 2006 00:46:43 +1000 [q] One suggestion I heard, if you do not want to modify the board, is to pulse width modulate the VGA signals. [/q] Wouldn't the PWM clock have to be 8 times the pixel clock instead of just 3 times? Not that 200MHz is such a big deal on a modern FPGA... [/q] -- <A HREF="http://members.optushome.com.au/jekent">http://members.optushome.com.au/jekent</A> Hi Jecel, I don't see why the PWM needs to be 8 bits long. It can be any length you want depending on the clock rate and the resolution required. The problem with PWM is that it is a decoded bit stream, so it's order N+1 (?) ie. doubling the number of bits in the PWM shift register doubles the number of colors but halves the resolution of the display for a given clock rate. I'm not sure how it would look either for long PWM values. You might have to come up with some sort of scheme to dither the pixels in the shift register so you have 101010 instead of 111000 for 50% duty cycle. John. Jecel Assumpcao Jr wrote: John Kent wrote on Tue, 08 Aug 2006 00:46:43 +1000 One suggestion I heard, if you do not want to modify the board, is to pulse width modulate the VGA signals. Wouldn't the PWM clock have to be 8 times the pixel clock instead of just 3 times? Not that 200MHz is such a big deal on a modern FPGA... -- http://members.optushome.com.au/jekent

Re: Text video driver by Unknown on Aug 8, 2006			Not available!
John, [q] I don't see why the PWM needs to be 8 bits long.[/q] Ooops - I overlooked that you were aiming for 64 colors and thought about 3 bits per component for a total of 512 colors. Then you would have to decode the 3 bits into an 8 bit PWM value. Your solution (2 bits per component) is the best tradeoff between results and complexity. -- Jecel John, I don't see why the PWM needs to be 8 bits long. Ooops - I overlooked that you were aiming for 64 colors and thought about 3 bits per component for a total of 512 colors. Then you would have to decode the 3 bits into an 8 bit PWM value. Your solution (2 bits per component) is the best tradeoff between results and complexity. -- Jecel

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