VGATonic Guide in Progress - Don`t Quit Your Day Job
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1. SPI Chip Select High You can send as many control characters as you want but only the last sent character to VGATonic will determine behavior VGA Tonic does not send any sort of acknowledgement other than perhaps changing the addressing on the screen you should see mode changes immediately Control Character Type I Changing Bit Depth and Resolution Writing control characters that start with 0 in the MSB will allow you to change resolutions and bit depths of VGATonic Our resolution modes differ from software resolutions or virtual resolutions To the monitor or display itself VGA Tonic will always present timing of 640x480 60 Hz so you don t have to worry about compatibility issues with lower resolutions as long as 640x480 works VGA Tonic does this internally it controls how long to wait on a pixel so the driver tells it how many bytes to expect by setting the mode Every drop in resolution is a halving of both width and height so FPS potential will be 4x as much for each reduction up to our maximum of 60 frames per second due to VGA timing Our bit depth modes are similar While on many video cards you would have to write say 16 or 24 Is to signal white in Black and White mode VGATonic will internally convert between color palettes so a single byte sent might mean 1 8 bit 2 4 bit 4 2 bit or 8 1 bit B amp W actual pixels written In essence every drop in color depth doubles the frame speed po2. Byte after c sets new background color d Erase all lines above current line e Enable the cursor f Disable the cursor l Erase current line line and place the cursor at the beginning of the row o Erase the current line from the beginning to the current cursor p Invert background and foreground color q Invert background and foreground color Special VGATonic Only Escape Codes Administrator Mode W W rite framebuffer mode pass through pixels from UART 150 at a time Z Send control character to VGATonic Position or Resolution or Bit Depth change m Become m aster of CPLD Disable external SPI writes and put Microcontroller in control r r elease CPLD Allow external SPI writes s elect CPLD Warn CPLD a new frame write is coming u u nselect CPLD Inform CPLD current frame write is done Special VGATonic Only Administrator Escape Codes Esc code lt 9600 Baud Serial Terminal Default 7 38400 Baud Serial Terminal Add one to LTC6903 PLL Scaler Subtract one from LTC6903 PLL Scaler amp VGATonic default PLL Scaler 0B01011110 Burn current PLL Scaler to EEPROM VGATonic Block Diagram io o E VGATonic e Block Diagram a e o o E gt 7 lt Microcontroller CPLD Graphics Core Serial Core Xilinx XC95144XL Atmel ATTiny 2313a SPI SPI Slave Terminal Emulator 777 i Calibration Async Serial Mea dupted P Display Core Administration Fr
3. Serial UGA Graphics Gard User Guide and Reference Manual Getting Started Providing Power VGATonic needs to be provided with 5V in order to work Connect VGATonic s USB Type B port to an open USB port on the device which will be using the VGATonic video card If there are no USB ports available or you would prefer to power VGA Tonic in another way please see the power labels on the PCB picture in the Appendix Note that if you don t power VGATonic from the board you will be using to drive it you should also connect a jumper between ground on the driver and ground on VGATonic to have a good reference See the Appendix for grounding points onboard VGATonic Connecting VGA Once power is provided to the board connect a VGA cable between VGA Tonic s VGA port and a VGA port on your monitor TV converter or other device Be careful you do not connect VGATonic to a device which provides VGA output you can destroy VGA Tonic or the other device Double check you are only connecting VGATonic to an output device or a converter which accepts VGA input If all is connected and your device didn t already autodetect VGA Tonic switch your device on and set the device s input to VGA You may need to read the user manual for instructions on how to do that for your unique situation VGATonic starts up with an all green screen if your device is connected to VGATonic and displays a green screen congratulations VGATonic is powered u
4. The PTC might take quite some time before resetting anyway you ve got time Hook up your Xilinx programmer or XSVF player but that is beyond the scope of this document ISE Webpack will program this part Initialize chain if it comes back with the right part the CPLD was soldered correctly If you re still going burn the CPLD with the firmware Congratulations the hard part is done REMOVE POWER BEFORE CONTINUING Framebuffer Memory Solder on 4 Mbit SRAM U3 Add decoupling capacitors C2 and C6 Programmable Oscillator Add the programmable oscillator U1 Add decoupling capacitors C11 and C12 Add SPI Pullup resistor R1 Microcontroller Add the microcontroller IC1 Add pullup resistors RA and R2 Add decoupling capacitor C4 Solder in headers to the ICP CHECK EVERYWHERE FOR SHORTS AGAIN Programming Part IT 1 Assuming everything is ready DO NOT APPLY EXTERNAL POWER Plug in the ICSP e fthere is a short the PTC fuse should get very hot disconnect quickly Fixthis condition before continuing The PTC might take quite some time before resetting anyway you ve got time 2 Programming the microcontroller is a 2 maybe 3 step process 1 Optional Calibrate the ATTiny s oscillator This is beyond the scope of this document but one way to do it is with an oscilloscope and Pepas Labs CalibrateATTiny85OSCCAL https github com pepaslabs CalibrateA Ttiny85OSCCAL 2 Program VGA Tonic firmware t
5. few games written in the past which used only ASCII Regardless this section houses details which a general user doesn t need to know to enjoy VGATonic but power users and folks who love to tweak and push the limits will find this information enlightening SPI on VGATonic SPI is the highest speed interface available to VGATonic and you will get the best framerates and highest quality output targeting SPI It has no minimum speed and the highest recommended speed is 59 7 MHz Faster speeds should work but they violate the setup time of the CPLD s buffers so you might have issues past 60 MHz As always keep connections short and clean while minimizing interference and if you see signal integrity issues try twisting wires and shielding your sensitive signals especially chip select with 5v power or ground jumpers SPI Control Characters For the SPI Framebuffer there are two main ways to manipulate VGATonic 1 The Chip Select Signal o Chip Select will reset the pixel counter to 0 0 the upper left to allow a new screen write o Jfa single pixel is written VGATonic will treat that pixel as a control character 2 Control Characters o One type of control character allows you to change VGATonic s mode o Another type controls cursor positioning allowing hardware acceleration Control characters work like this SPI Chip Select Starts High then SPI Chip Select Low Send exactly one byte of data this is the control character
6. monitor settings to ensure your monitor is set to VGA input on the port VGATonic is connected to Most if not all monitors which adhere to the VGA standard or VESA modes will syne to VGATonic but we are unable to test every individual device to ensure perfect compatibility It s possible the PLL is set incorrectly too see the section on resetting the PLL to factory below if you think this is the case usually the monitor will have a notice or indication it cannot sync Analog monitors will likely provide the best user experience if available My Monitor Won t Sync to the VGATonic Signal From factory VGATonic is 0119 out of spec from the VGA clock a standard monitor will only have issues with between 0 and 49 displayed pixels total in our top mode If you think you have changed the clock setting inappropriately in Administrator Mode you can reset the PLL to factory easily Power cycle connect over serial at 9600 baud 8 N 1 and issue the following commands Escape amp to reset the LTC Calibration bit to factory Escape to burn the factory bit to EEPROM My Serial Connection Isn t Working VGATonic starts in 9600 baud 8 N 1 mode but can be changed to 38400 mode Try using the speed you aren t currently connecting at if that doesn t work power cycle VGATonic and connect at 9600 baud 8 N 1 Be sure you are using 3 3V serial RS 232 voltages can destroy VGATonic VGATonic Won t Respond to SPI or Serial Writes Firs
7. PLD a new frame write is coming u u nselect CPLD Inform CPLD current frame write is done Asynchronous Serial Framebuffer We couldn t leave the microcontroller alone without one last essential feature a Serial Framebuffer Mode Since VGATonic s top serial speed is a modest 38400 baud most resolutions and bit depths are more of a slideshow mode so calling it a framebuffer is charitable However if your video application can stand 80x60 resolution you can get 5 2 frames per second in Black and White or 2 6 frames per second in 2 bit color at 38400 baud For most video applications you are better off using SPI Serial applications are best served by the VT52 emulator but for specific applications such as digital signage the framebuffer mode is very nice to have If you would like to try the serial framebuffer this is how the protocol works 1 Optional Set mode resolution as detailed in the Graphics Control Mode section above 2 Send VGATonic an Escape character ASCII 27 1 VGATonic responds gt ASCII 62 If VGATonic doesn t respond with anything you can send escape characters until you get DCI ASCII 17 or gt ASCII 62 it likely was halted during a framebuffer write If VGATonic responds with nonsense you are likely in the wrong serial speed either 9600 baud or 38400 baud See the administrator mode section for how to change speeds or use the other speed 3 Send VGATonic a W characte
8. amebuffer Lodi Handler Driver pe gt 2 ES ss Pg x O i 0 0 iF la a di HF EREHE E pe rot FF EE B 8 Y YY Y Y Programmable Clock 4 Mbit Framebuffer Linear Technology ISSI IS61LV5128AL 10 LTC6903 jndino VODA Signal Key User Interface Signal Data Clock Signal Control Signal High Resolution PCB Stars Mark Power Ground Black Ground Yellow 3 3 Volts Red 5 Volts Only Apply Power to USB OR One 5V Pin never both mol LL pH EE EH E LEE LE LE T VGA Tonic Start Up Sequence 1 ATTiny 2313a microcontroller sends control bytes to LTC6903 Programmable Oscillator to set the Display Core Clock o With default firmware this will be 50 344 MHz or almost exactly 2x the 640x480 VGA Clock of 25 175 MHz Microcontroller grabs control of VGATonic s Display Core VGATonic will ignore all external SPI writes 1 Sets mode to 160x120 in 8 bit color 2 Draws acompletely green screen and sets the font color if later needed Microcontroller gives up control of the Display Core to the external SPI interface
9. attempting to calibrate VGATonic However if you would like to change VGATonic s oscillator clock speed you can use these sequences to try new speeds Escape to increase the calibration by 1 see LTC6903 datasheet for details Escape to increase the calibration by see LTC6903 datasheet for details Escape to burn the new calibration to EEPROM Graphics Control Mode VGATonic exposes the control characters available to SPI to the terminal emulator as well Hardware acceleration works but utility is diminished from SPI since framebuffer mode requires a multiple of 150 byte sends which is 1 200 black and white pixels a far cry from the 2 pixel minimum write in SPI at 256 colors Bit depth and resolution changing is more useful You need to ensure that the microcontroller is in master mode See the Control Character section in the Hacker s Guide for details Here is an example sequence Escape m Optional yet mandatory at start set master mode Escape Z Control byte incoming Send exactly one byte of data representing a control character All Unique VGATonic Escape Codes Administrator Mode W W rite framebuffer mode pass through bytes from UART 150 at a time Z Send control character to VGATonic Position or Resolution or Bit Depth change m Become m aster of CPLD Disable external SPI writes and put Microcontroller in control r r elease CPLD Allow external SPI writes s s elect CPLD Warn C
10. e are board dependent and go by the board s naming conventions You can of course change these in the drivers but these are what we used and must be used if you do not change code Chip Select CS Label MOSI Label SCK Label Raspberry Pi 2 Model B 22 BCM 25 BCM 10 MOSI BCM 11 SCLK Odroid C1 103 107 BeagleBone Black GPIO_48 SPIO_D1 Intel Edison 49 43 SPI 2 TXD Arduino Uno 9 11 For a description of the SPI protocol in order to write your own driver please see the Hacker s Guide or take a look at some of the code in our repository Asynchronous Serial Modes VT52 Compatible Terminal Emulator VGATonic includes a VT52 like terminal emulator which provides a subset of VT52 escape codes as well as VGATonic specific and unique do not try on a working VT52 escape codes and administrator escape codes It also includes a single font in memory When VGATonic starts up it quickly initializes the oscillator and prints a green screen and puts the SPI bus in charge of the VGA Output In order to use the terminal emulator you must connect over serial and put the terminal emulator in charge Connect over TTL Serial at 9600 baud 8 N 1 please see your serial device s manual for information on how to connect it is beyond the scope of this document On a Macbook I use a USB to Serial Adapter and the screen program in a terminal to connect The TX and RX pins onboard VGATonic should be used to conn
11. e the screen look torn Noise on the chip select line on the other hand might show up as rapidly changing modes or partial writes Most new monitors allow you to fine tune for phase and clock frequency check your monitor settings and try to adjust both sliders Let VGATonic warm up before calibrating your monitor VGATonic allows you to adjust the value of the onboard LTC6903 programmable oscillator easily over asynchronous serial You can try adjusting the clock up and down and see how your monitor or TV reacts When you find an acceptable setting you can burn it to EEPROM See the Hacker s Guide for more information Hacker s Guide VGATonic was initially developed for Hackaday s 2014 and 2015 Prize Competitions so a key philosophy in the design is hackability and openness This led me to add fun features like a programmable oscillator and easy to program silicon like a microcontroller and a CPLD to the mix along with unpopulated prototyping pins and space to add switches When all was said and done VGATonic ended up with four main components the CPLD the Microcontroller the Programmable Clock and a 4 Mbit SRAM to hold our display data The firmware to the CPLD and the Microcontroller are open source and I ve included examples of protocols and framebuffer drivers in Linux for the SPI and the Asynchronous Serial framebuffers Of course the VT52 like Terminal Emulator is also available surely there have been more than a
12. ect to serial ensure you properly connect your serial device Escape m Master mode Escape s Select CPLD Escape Z r Set to 8 bit color depth at 160x120 resolution since we don t know what we were in To ensure the serial connection now has control of the display driver you can now send ASCII characters to VGATonic and see if they are printed on your screen Escape E capital E clears the screen and moves the cursor to the upper left If it works congratulations The terminal emulator is simply the easiest way to add VGA output to a project as the serial protocol is widely supported at 9600 baud Any microcontroller or TTL serial output that supports 8 N 1 serial at 3 3 volts can communicate with VGATonic and display characters and colors on the screen It is particularly useful as a debugging output window for projects with serial available A complete copy of all codes supported can be found in the Appendix Information on how to use high speed 38400 baud mode is in the Administration section below To give control of the display driver back to the SPI connection either power cycle VGATonic or use this command sequence over serial Escape Z r 0 Set to 8 bit color depth at 640x480 resolution since we don t know what we were in Escape u Unselect CPLD Escape r Release master mode Asynchronous Serial Framebuffer While using the terminal emulator VGATonic has special escape codes which allow you to direc
13. in software which is beyond the scope of this booklet Is SPI Correctly Output Due to hardware differences we can t test every SPI implementation but please ensure you are getting SPI as expected from your hardware What s Your Ground Reference If VGATonic is physically separated from its driver run a jumper between ground as short and or thick as possible on the two modules to have a common reference voltage Is Chip Select Working Properly Chip select is fraught with issues on many boards it is easiest to use a software controlled chip select because VGATonic does up to 307 200 byte writes For that reason use software chip select for control Additionally double check CS signal integrity My Picture Isn t Perfectly Stable There is Pixel Drift and or Jagged Lines VGATonic prioritized hackability over perfect stability eschewing a crystal oscillator for a programmable oscillator That opens up more future features but you may see minor dot crawl or other analog artifacts on your monitor We also drove to keep costs low and VGATonic managed to arbitrate reads and writes in single buffering onboard instead of more expensive schemes like double buffering Anyway there are things you can try in order to clean up before you beg for HDMI Lower bit depths toggle outputs multiple time based on a single write while more bits per color will toggle more slowly If you can use higher bit depths Noise on the MOSI line can mak
14. nd Intensity where 1 is bright 2 Bits HL HL HL HL 4 Pixels of high low 1 Bit IIIIIIII 8 Pixels of 1 white and 0 black Since the Chip Select controls the reset for writes you can stop writing at any time after at least 2 bytes are sent This is useful if for example you are redrawing a cursor at the top of the screen In conjunction with the hardware acceleration it means VGATonic can quickly update any position in the screen even if a full screen refresh would be very slow A combination of hardware acceleration and non fullscreen writes can actually open up different accelerated resolutions consider using the acceleration to jump down a number of rows then only writing the number of rows needed for your virtual resolution then pulling CS high again If you are only doing partial screen refreshes this means you can effectively update the screen faster than your SPI speed would otherwise support Asynchronous 3 3v Serial on VGATonic Onboard VGATonic is a 3 3v compatible serial interface to the microcontroller It exposes 9600 baud and 38400 8 N 1 serial modes at TTL voltages and allows you to control administration features of VGATonic and it also manages to fit a VT52 Compatible Terminal Emulator and a framebuffer onboard VT52 Terminal Emulator VGATonic s terminal emulator is technically always running as soon as VGATonic is turned on and the startup routine has completed However the microcont
15. ng a single pixel with a 1 in the MSB will cause the remaining bits to become the MSBs of the address bits of the next pixels written Note that each resolution and bit depth reduces the number of addresses that are used Acontrol byte of 11110011 would use bits 1110011 in the address MSB dropping the first 1 There is an implied 00 added onto the end as the addresses themselves are 10 bits e For 640x480 a control character of 11100000 would set the next write at row 0b0110000000 or row 384 e For 160x120 a control character of 11100000 would set the next write at row 0b01100000 or row 96 This is how it works o Start at 0b0110000000 then gt gt 2 320x240 shifts 1 160x120 shifts 2 80x60 shifts 3 SPI Framebuffer The SPI framebuffer is extremely straight forward and was designed with the highest possible throughput in mind The only overhead is the chip select which pulls double duty to reset VGATonic s writing buffer to 0 0 the upper left pixel The protocol is as follows SPI Chip Starts High SPI Chip Select Low Send more than one SPI byte up to 307 200 for 640x480x8bpp SPI Chip Select High resets to 0 0 The number of pixels contained in each SPI byte is dependent on your color depth The base mode is 8 bits per color so every byte will represent a single pixel All four accelerated depths look like this internally to VGATonic 8 Bits RRRGGGBB 1 Pixel 4 Bits RGBI RGBI 2 Pixels or RGB a
16. no shorts triple check it apply power Assuming the fuse doesn t trip try hooking up the VGA output A green screen means all the programming worked congratulations Try interfacing with VGATonic over Asynchronous Serial and or SPI that will be the final message on whether your VGATonic build was a successful one About VGATonic and its Builder PK If you re anything like me you ve got a bunch of dev boards and single board computers stored somewhere in your house That pile was getting pretty big when I got the idea for VGATonic VGA output I could add to some of the headless parts I d collected Fortuitously the Hackaday Prize 2014 was just kicking off those two threads tied together and VGATonic was born I finished a minimum viable project in 2014 working 640x480 in 256 colors on an Arduino and an Intel Galileo in Arduino Mode but didn t push for a product let alone a completed project Admittedly my effort was weak on the order of I have proven it can be done but no further Motivation waned for a while until I saw a soldered VGATonic on my desk a few weeks into the Hackaday Prize 2015 and I sat down and wrote a Linux framebuffer driver for the Raspberry Pi When I played Doom on VGATonic for the first time the motivation came rushing back The rest as the saying goes is history 2015 has been dedicated to bringing example graphics drivers to lots of new single board computers and microc
17. o burn EEPROM fonts initial calibration for LTC6903 1 It s simple in your IDE remove the comment from the line define EEPROM UPDATE 1 Uncomment when you want to write EEPROM otherwise leave this alone 2 Ifyou calibrated the oscillator change the character in OSCALSPEED from default K in the file utilities ino eeprom update byte uint8 t OSCALSPEED K 3 Once the line is removed upload the firmware from the Arduino IDE to the microcontroller over ICSP 3 Program VGATonic s non EEPROM code 1 Just add the comment back to the line 2 Once the line is added back VGATonic will fix the font lookup and add all of the code to support the framebuffer and terminal emulator 3 REMOVE POWER BEFORE CONTINUING VGA Output Stage Add the VGA Connector 2 Add VGA output resistors R5 R6 R7 R8 R9 RIO R11 R12 R13 External SPI Interface Add male headers to P2 labels SCK MOSI MISO and CS 2 Add SPI Pullup resistor R3 External Serial Interface 1l Add male headers to P1 labels RX and TX Optional For hardware hacking or alternative modes these components might be useful Add the optional Wing Style female headers in P8 P7 P10 and P9 2 Add the optional user switches to SW1 1 Add resistors R20 R21 R22 3 Add the RCA Output Stage 1 Solder in the RCA Jack 2 Add output resistors R14 R15 R16 R17 R18 R19 If you re sure there are
18. ontrollers along with hardware acceleration lower resolution modes and lower bit depth modes I also added lots of features to the microcontroller and the all important asynchronous serial modes which give out of the box framebuffer and terminal emulator support to probably but who can count thousands of parts made over the last 40 years As for me I live in Silicon Valley and work as a software engineer I ve been at the same firm for the last seven years I m married with a not yet two year old daughter and a dog my wife and I jokingly call our son When I m not working on hardware projects I maintain a website at http dqydj net that includes lots of hacks of the software variety Appendix VGATonic Escape Codes VT52 Compatible Escape Codes Hit escape then hit the following character to execute the commands A Move the cursor to beginning of line above B Move the cursor to beginning of line below C Move the cursor right by one D Move the cursor left by one E Clear the screen and place the cursor in the upper left corner H Move the cursor to the upper left corner I Move the cursor to beginning of line above J Erase all lines after our current line K Clear the current line from the current cursor position M Delete the current line Y Goto Coordinate mode first will change line number then cursor position both ASCII 32 b Byte after b sets new foreground color c
19. p and working You are now ready to pick a mode and start using VGATonic as a framebuffer or terminal emulator 2 Connect VGA m m CE s Leones i V or 1 Apply Power KLAS PEEL 3 Connect SPI or Serial VGATonic Usage Modes Connecting SPI and Serial VGATonic has two main forms of communication which are available 5v 3 3v 2 5v SPI or 3 3v Asynchronous Serial also known as TTL RS 232 or TTL Serial Using those protocols three display modes and one administration mode are available SPI e Framebuffer TTL Serial e Framebuffer e VT52 Compatible Subset Terminal Emulator e Administration Mode You may use Serial and SPI at the same time although only one can be the master at once SPI Modes SPI Framebuffer The only available SPI mode is the SPI framebuffer The easiest way to get started with SPI is to use the drivers we provide on Github and one of our supported boards although we have provided enough examples for you to port to the platform of your choice As of this printing we have provided driver examples for the Raspberry Pi 2 Model B The Odroid C1 the BeagleBone Black and the Intel Edison with Arduino Breakout Board We have also provided user mode drivers and Arduino driver code The SPI header onboard VGATonic contains SCK MOSI MISO and CS Chip Select pins but MISO can go unconnected The pins in the tabl
20. r ASCII 87 1 VGATonic responds with ACK ASCII 6 4 Send VGATonic 150 Bytes 1 After last byte VGATonic responds with DCI Device Control 1 ASCII 17 5 Repeat as desired pump pe BU Viv wp Building and Programming VGA Tonic Want to build VGATonic from scratch That s the spirit Grab our latest hardware on Github and fire up your iron Prerequisites Steady hand soldering iron parts Xilinx Programmer or XSVF Player USBTiny ISP or other Atmel programmer for ICSP Xilinx ISE Webpack Software Recent Vintage Arduino IDE with arduino tiny installed and all hardware serial files commented out https code google com p arduino tiny The CPLD Solder on the CPLD U2 Solder on the decoupling capacitors next to the CPLD C1 C3 C5 C7 C8 C9 C10 and the 6 pin header needed to program the CPLD these pins are marked TCO TCK TMS TDT GND and 3 3V and labeled P4 Check for shorts between power and ground ensure your chip 1s oriented correctly etc The Power Supply Solder on capacitors C15 C14 and C13 Add fuse F1 Add 3 3v Regulator U4 Finally solder on USB B power jack J1 As always check for shorts double check all your work check orientation etc Programming Part I Assuming everything is ready Apply power e If there is a short the PTC fuse should get very hot but shut down the board quickly Fixthis condition before continuing
21. roller will not be the master of the Display Core by default this sequence will grab control it will not hurt VGA Tonic if it already has control though perhaps from a past terminal session Escape m Master mode Escape s Select CPLD Escape Z r Set to 8 bit color depth at 160x120 resolution since we don t know what we were in Escape E Optional clears the screen After you have control of the terminal emulator attempt to send ASCII characters to the screen to verify you are now the master of the Display Core You now are using a terminal emulator with only 128 bytes of RAM VGATonic supports 40 characters by 15 columns and has one built in font VGA Tonic supports most VT52 escape codes although a few are unimplemented because the microcontroller only has enough RAM to keep track of position status the UART ring buffer and the current line However it does allow you to change lines it will just enforce line clears for every line change It also supports 256 colors for background and foreground colors an improvement on the VT52 compatible 16 color modes As for typical ASCII backspace and or delete are supported as well as the newline carriage return Other ASCII characters are ignored except of course escape ASCII 27 For a full listing of VGA Tonic escape codes see the Appendix Giving control back to the external SPI interface is really just the reverse of grabbing control Here is an e
22. t ensure the bus you want is the master of the Display Core After a power cycle SPI will be in charge see the section on the VT52 Compatible Framebuffer for information on how to change it VGATonic is Working but My Colors Are Suddenly Inverted Don t Match What is Expected If VGATonic was previously working the most common cause of this is poor signal integrity the chip select line is particularly sensitive to interference The easiest way to clean it up is to twist 5v power or ground supplies around sensitive signals You may need to power cycle SPI Won t Respond SPI is Causing Garbled Output There are many things to check here so this is not a complete list e How fast is SPI Running VGA Tonic is in spec up to 59 7 MHz SPI although we have tested at up to 62 5 MHz successfully How is Your Signal Integrity At faster speeds long wires become antennas Ensure your wires are as short as possible with strong and firm connections to both your device and VGA Tonic It usually helps to use twisted pairs wrap power or ground signals around your SPI signals to cancel out some coupling issues Here is some example routing with a BeagleBone Black Note USB is not used for power in the image if it is only add ground connections Which SPI Mode is Running VGATonic works best in SPI mode 3 or 0 on most hardware but because SPI is a loose standard please try 1 and 2 if that isn t working You will need to make this change
23. tential For example a 25 MHz SPI part can do about 10 frames per second in 640x480x8bpp but 20 frames per second at 640x480x4bpp Control bits for changing bit depth and resolution work like this where location 7 is the MSB and 0 is the LSB or last bit sent in the byte Bits 6 5 and 4 are ignored write whatever you like Bits 3 and 2 Bits Per Pixel Color Depth 00 8 Bits Color Per Pixel 256 Colors e 01 4 Bits Color Per Pixel 16 Colors e 10 2 Bits Color Per Pixel 2 Grays Black White e 11 1 Bit Color Per Pixel Black and White Bits 1 and 0 e 00 640x480 e 01 320x240 e 10 160x120 e 11 80x60 You can of course change both at the same time 500000110 tells VGATonic to set 4 bits per pixel color at 160x120 resolution Note that control pixels are wonky on single board computers or things without cycle accurate timing if they are blocked from an SPI write for example during a video or game where the CPU is too busy to service another SPI write you may need to send more than one mode change to get it through Setting the mode multiple times even if all are successful won t hurt VGATonic This is part dependent and beyond the scope of this document but if you don t see responses from a single board computer this is the first place to check Control Character Type II Hardware Acceleration VGA Tonic allows for hardware acceleration it can skip to certain rows to begin writing new pixels Writi
24. tly write pixels to the screen While 640x480x8bpp will be painfully slow even at 38400 baud with modest resolutions like 80x60x1bpp you can get a usable framebuffer even over serial The escape characters needed are printed in the Appendix Please see the Hacker s Guide and the python example provided on Github for a description of how to write directly to the framebuffer over serial Administration Mode The terminal emulator also has an administration mode which allow custom settings for your VGATonic A listing of all codes can be found in the Appendix provisions are included for toggling the serial speed between 9600 and 38400 baud as well as adjusting the PLL on the programmable clock in order to better sync to your monitor Please see the Troubleshooting Guide for more on calibration Troubleshooting Guide Sometimes things don t work as expected Here is a list of common problems and things to check in order to attempt to fix them VGATonic Won t Power On If USB is connected properly connect another device to the USB port you are using in order to check if power is coming from the USB port Alternatively VGATonic can be powered through other pins on board see the Appendix for details When not using USB always connect ground first only use 5V pins to provide power and only use one power source at a time VGATonic Won t Display Over VGA First check VGATonic is powered then try a different VGA cable Also check your
25. xample sequence to put SPI back in charge of the Display Core Escape Z r 0 Optional sets to 8 bit color depth at 640x480 resolution or whatever you want Escape u Unselect CPLD Escape r Release master mode Administrator Mode VGATonic has an administrator mode which allows you to fine tune the clock speed of the LTC6903 to improve compatibility with your display and it also allows you to toggle between 9600 and 38400 baud 8 N 1 serial It is important to note that VGATonic always starts in 9600 baud mode for newer parts it s suggested to change to 38400 baud immediately To enter administration mode connect over serial then use the escape sequence Escape ASCII 27 37 to open up options lt 9600 Baud Serial Terminal Default 7 38400 Baud Serial Terminal Add one to LTC6903 PLL Scaler Subtract one from LTC6903 PLL Scaler amp VGATonic default PLL Scaler 0B01011110 Burn current PLL Scaler to EEPROM Administrator mode is most useful for changing serial speed but it can also calibrate the onboard programmable oscillator the LTC6903 By default VGA Tonic programs the part at roughly 50 344 MHz If you have changed calibration and your monitor will no longer attempt to sync you can reset the oscillator like this Escape amp to reset the LTC Calibration byte to factory Escape to burn the factory byte to EEPROM We suggest trying to calibrate your monitor to VGATonic first before
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