A VGA Arduino Uno Shield or Adafruit Feather Wing
640x480 - 512 colours
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The VLSI VS23S040 is the successor of the trusted VS23S010 composite video chip with framebuffer. This Shield/Wing uses the VS23S040 to generate VGA signals or composite video.
Currently it is running as 4x composite video output with resolution NTSC 320x200 in 256 colours and PAL 300x240 in 256 colours.
I plan to get it running in the future as VGA with 640x480 resolution with 3bit per RGB to generate 512 colours.
SCH_P42-VGA_ver2.pdfSchematics PDF (Done with KiCAD)Adobe Portable Document Format - 133.28 kB - 01/30/2021 at 01:19 |
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BOM P42-VGA_ver2.pdfBill of materialAdobe Portable Document Format - 424.75 kB - 01/30/2021 at 01:19 |
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AD_P42_VGA_rev2.pdfAssembly DrawingAdobe Portable Document Format - 21.57 kB - 01/30/2021 at 01:19 |
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The idea is to have messages from 2 serial ports being displayed and scrolled up. I would call it semi-duplex, as ideally one side sends a command/line and the the other side. If both sides send characters at the same time, they get mixed with each other in the same line. Different colours for the 2 sides are used, so it is visible if that happens.
HW Setup:
Arduino Mega with P42 Video4 VGA Shield
Standard serial port setup as SERIAL 115200 8N1
2nd serial port setup as SERIAL1 38400 8N1 (this is also a hardware serial port on the Mega on pins 18:TX 19:RX). The baudrate is set to 38400 to be operational with the Arduino SoftwareSerial library as well. For the 2nd serial port a TTl-UART adapter is required with connections to RX, TX and GND.
SW Setup:
!!! The Arduino Serial Monitor is not suitable for this setup. A proper terminal software is required, I use two instances of TeraTerm, configured with the correct serial settings, local echo and transmit CR+LF.
The display shows the 2 different sources in light and dark colour.
Description:
The global variables ScreenX and ScreenY as well as the function printlineXY() are the heart of this demo.
ScreenX, ScreenY point to the coordinate of the screen where the next character will be printed. Function: byte printlineXY ( byte channel, char* Text, byte colour, bool ln )
Paramters:
byte channel: is the video channel used for display; can be one of CH0, CH1, CH2, CH3.
char* Text: pointer to a string, null terminated. To print a single character, the character + a NULL byte need to be content of the string. Maximum string length is the remainder of the current line + a full additional line as only one linebreak is currently implemented.
byte colour: a 8-bit colour value picked from the colour table in the user guide.
bool ln: of TRUE a CR+LF is performed to start a new line after the string got printed. byte return value: currently always 0.
At the bottom of the screen, if the last line is full or LF = TRUE, a line scrolling is implemented to make room for the next line of text. Implemented control codes:
0x08 : Backspace, the last character gets deleted to free the area for the next character to be printed, so technically it is a 'delete char'
0x0A : LF Linefeed, cursor go to next line, but same horizontal position 0x0D : CR Carriage return, cursor goes to the beginning of the current line
SW repository
https://github.com/wolfgangfriedrich/P42-VGA/tree/master/Code/P42VGA_V4Text
Revision 2 of the board is running as planned. I replaced the trusted level shifter buffer 74LVC4245A with a TI TXS0108, which is automatically bi-directional. The bi-dir feature is not needed here, but a good exercise for future use. Attention has to be paid, as there is also a TXB010x family which works better with fully driven signals. The TXS0108 is on order for open drain signals, e.g. the MISO sinal on SPI slave devices.
Channel 0 is on the RCA connector, channels 1,2,3 are on the VGA connector, accessible with a VGA to 3x RCA cable.
Soldering the BGA was amazingly easy. I use some low-temperature solder paste and a boatload of flux with my hot air pencil and everything aligned itself into place. How do I know that I have good contact? Measuring with a multimeter in diode mode, I see a diode drop of ~0.55V between every IO and Vcc. Now I have to solder all the other parts and start talking to the chip. Then comes the hard part, writing good driver software and config code...
The other parts went on just as easy... Well, mostly.
This looks like a nice schematic, all signals are there (sigh):
The board needed some wire surgery, but in the end it works and now I have 16Mbit of SPI Flash for character sets and images.
These guys really have a bag of tricks! I guess it takes a while to understand the finer details of this ingenious chip design. I'm thinking of buying some and make a breakout board.
What kind of solder paste and flux did you use?
Try contacting VLSI sales, they sent me samples of the S010 and S040.
Yes, the datasheet is a handful, but there are some very good articles in the forum, explaining stuff in detail. And sample code, which helped me a lot. When I saw the chip, I also thought about a breakout board, but never followed up on it. I even asked around about the style.
https://www.element14.com/community/polls/2907
My shield wing turned out to be OK, so I don't need a breakout any more. I am using low temperature MG Chemical M3 #4902P solder paste for my prototypes. It is lead free and has a melting point of ~140degC. For production I use Chipquik NC191SNL15 lead free paste, very easy to work with. For flux, I have Chipquik SMD 291 no clean tack, which is great gooey stuff, but ugly residue when I don't clean it!? I like clean boards.
That's a very interesting chip for retro-computing! Do you know where it's commonly used?
By the way, you mention 640x400 in the project title and 640x480 in the details. There certainly enough RAM for the once-popular 800x600 format but are there other limitations?
I briefly browsed the data sheet and noticed that there is a memory-move command - nice! This means that even text mode with scrolling should be feasible. An 8bit µC playing "character generator" will still be a bottleneck, but that's likely still OK for that 80s feeling ;-)
Edit: I had a look at VLSI - they have a maker/small company friendly store (single quantities, PayPal!), and the team looks like it consists of the kind if Finnish people I've learned to value:
Yes, it is a family of 2 interesting chips. Thanks for pointing out the error with the resolutions. I'll fix that to ...x480 because... VGA. The RAM distribution is 1Mbit per channel as the chip is basically 4 dies of VS23S010 in one package. Higher resolutions does decrease the colour depth as well.
My P42-Display project #NTSC/PAL Video Display Shield uses the VS23S010 chip and I have seen this one in one retro platform but have no idea about commercial applications.
My demo of the bouncing AMIGA ball uses the memory move command. The memory mapping is very unusual as the source block does not allocate a consecutive block of RAM, but has enough bits between the lines to fill up a full line! The character map could live in the free part of the video RAM as well and use the block move for fast display.
VLSI is a nice company, they shipped directly to Elecrow for a small build for me. Panu and the other guys are super helpful in the forum.
Thanks for the explanation and details! The VS23S0x0 are a bit like 80s ingenuity with today's silicon and density (it address-space / control trade-off reminds me a bit of the Apple II).
I didn't notice the 4-dies-in-a-package thing. I'll check the datasheet again to learn why SPI still works!
MagicWolfi
fjkraan
PK
Just4Fun
No more reply, 4 comments deep ;(
I think there was a comment from Panu in the VLSI forum about the S040 dies.
SPI works tricky, as everything else in the chip. There is a register to disable access to any of the 4 register/memory sets. So you can write all 4 or only selected ones at the same time, same as 4 identical chips connected to an external SPI bus. For read commands only one can be enabled to give a meaningful answer.