Summary of HCS08 VGA Output
This reference design generates VGA signals using the Freescale MC9S08SH16VTJR 8-bit microcontroller running at 40MHz. It produces a 640x480 resolution signal with a 60Hz refresh rate and 25.175MHz pixel clock. The system utilizes an internal Frequency-Locked Loop for clock precision and generates video through an infinite loop that draws lines divided into 16 parts, storing color data in RAM with 1-bit per channel support for eight basic colors.
Parts used in the HCS08 VGA Output Project:
- Freescale MC9S08SH16VTJR 8-bit microcontroller
- Central Processor Unit (CPU) with 40MHz speed
- Frequency-Locked Loop (FLL) module
- Internal clock source
- Analog color signal generator (0-0.7V range)
- TTL synchronization signal generator
- RAM for storing color arrays
- HX register for array pointers
- A register for line count
This reference design is a simple VGA signal generation that uses the Freescale’s MC9S08SH16VTJR, which is an 8-bit microcontroller that has Central Processor Unit (CPU) speed of 40MHz with a maximum bus frequency of 20MHz. It has an internal clock source module containing a Frequency-Locked Loop (FLL) controlled by internal or external reference. Its precision trimming of internal reference allows 0.2% resolution and 2% deviation over temperature and voltage with 1.5% deviation using internal temperature compensation. The simplest instructions such as NOP take 1 bus cycle, the other instructions take more cycles, and for example RTS takes 6 bus cycles.
The VGA signal has 5 components that include horizontal synchronization, vertical synchronization and three analog color signals. The analog color signal range is 0-0.7V with 75Ω impedance and sync signals are TTL signals. The device has a refresh rate of 60Hz with 640 x 480 resolutions, and the pixel clock is 25.175MHz. The display refresh rate is therefore slightly lower, somewhere around 57Hz. The implementation for video signal generation is in the form of an infinite loop where one loop cycle is equal to one video frame. During every frame the video signal is generated line by line. A subroutine was created that draws multiple lines, where the number of lines is expected in the A register. Every line is divided into 16 parts. Colors of these parts are stored in RAM. Pointer to this array is expected in the HX register. Each of the 3 color channels is 1 bit only having 8 available basic colors.
For more detail: HCS08 VGA Output
The VGA signal has 5 components that include horizontal synchronization, vertical synchronization and three analog color signals. The analog color signal range is 0-0.7V with 75Ω impedance and sync signals are TTL signals. The device has a refresh rate of 60Hz with 640 x 480 resolutions, and the pixel clock is 25.175MHz. The display refresh rate is therefore slightly lower, somewhere around 57Hz. The implementation for video signal generation is in the form of an infinite loop where one loop cycle is equal to one video frame. During every frame the video signal is generated line by line. A subroutine was created that draws multiple lines, where the number of lines is expected in the A register. Every line is divided into 16 parts. Colors of these parts are stored in RAM. Pointer to this array is expected in the HX register. Each of the 3 color channels is 1 bit only having 8 available basic colors.
For more detail: HCS08 VGA Output
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What microcontroller is used for this VGA signal generation?
The project uses the Freescale MC9S08SH16VTJR 8-bit microcontroller. -
How fast is the Central Processor Unit in this design?
The CPU operates at a speed of 40MHz with a maximum bus frequency of 20MHz. -
What resolution and refresh rate does the display achieve?
The device supports 640 x 480 resolutions with a 60Hz refresh rate. -
What is the pixel clock frequency required for this implementation?
The pixel clock frequency is set to 25.175MHz. -
How many basic colors are available with this color configuration?
There are 8 available basic colors since each of the 3 color channels is 1 bit only. -
Can the internal reference be controlled by external sources?
Yes, the internal clock source module can be controlled by either internal or external references.
