PIC PAL Video Library using pic18f4620

If you are into PICs, you maybe tried one day or another to build a software video processor, either for fun or for a project.
If you tried to generate video signals, you surely know some of this web pages :

• Rickard Gunees PIC PONG page : http://www.rickard.gunee.com/projects/
• Eric Smith video clock : http://www.brouhaha.com/~eric/pic/pictock.html

This projects are fun, but I wanted to build a general purpose software video processor, to drive a TV screen just like a GLCD could be.

I kept the idea to use a 2-resistor ladder as a fast and cheap digital to analog converter, and started to work on the software.

PIC PAL SOFTWARE VIDEO LIBRARY

Since the video screen has to be mapped in memory, only PICs with enough RAM are concerned, that’s why the PIC PAL Library is for PIC18 family only.

The PIC must be clocked at 32 Mhz with a 8 Mhz crystal, to get the 64 µs horizontal synchronization timing of the PAL system.

The library generates a 625 lines interlaced PAL video signal, and can display up to 248 vertical lines of 128 pixel. Any video display device with a PAL video composite input should be able to display the picture generated by the PIC.

Because timing is critical, the part of the software producing the video uses in-line assembly mixed with C.

You can download the full mikroC project, including the library source code.

Here is the user’s manual of the PIC PAL Library :

INITIALIZATION

 

PROTOTYPE	void    PAL_init(unsigned char y)
PARAMETERS	y : number of vertical lines, up to 128
RETURNS	nothing
DESCRIPTION	prepare the PIC PAL video library the more vertical lines you want, the less memory & MPU power you haveWarnings : this library takes control of TIMER 0 and associated interrupts ! this library takes control of the PORTD !
REQUIRES	the file PAL_library.hmust be included in user’s source code.specified hardware with 2 resistors, see schematic the device must be clocked at 32 Mhz
EXAMPLE	PAL_init(128) ;

Video control

 

PROTOTYPE	void    PAL_control(unsigned char st, unsigned char rd)
PARAMETERS	st : PAL synchronization control PAL_CNTL_START : start PAL synchro PAL_CNTL_STOP : stop PAL synchro (free all MCU power)rd : rendering control PAL_CNTL_BLANK : only borders are displayed (free a part of MCU power) PAL_CNTL_RENDER : full video is rendered, with borders and picture (most of MCU power is required)
RETURNS	nothing
DESCRIPTION	control the video generationwhen the PAL synchro is started, the unsigned long global variable PAL_frameCtr is incremented 25 times per second.
REQUIRES	PAL_init() must have been called
EXAMPLE	PAL_control(PAL_CNTL_START, PAL_CNTL_RENDER) ;

FILL SCREEN

 

PROTOTYPE	void    PAL_fill(unsigned char c)
PARAMETERS	c : filling pattern
RETURNS	nothing
DESCRIPTION	fill screen with pattern c use 0 to clear the screen, 0xff to paint the screen in white
REQUIRES	PAL_init() must have been called
EXAMPLE	PALL_fill(0) ;

SET SCREEN BORDER COLOR

 

PROTOTYPE	void    PAL_setBorder(unsigned char border)
PARAMETERS	border : either PAL_COLOR_BLACK or PAL_COLOR_WHITE
RETURNS	nothing
DESCRIPTION	change the screen border color surrounding the picture
REQUIRES	PAL_init() must have been called
EXAMPLE	PAL_border(PAL_COLOR_BLACK) ;

SET PIXEL

 

PROTOTYPE	void    PAL_setPixel(char x, char y, unsigned char mode)
PARAMETERS	x : pixel column, from 0 to 127 y : pixel row, from 0 to the number of lines – 1 mode : pixel color, either PAL_COLOR_BLACK,  PAL_COLOR_WHITE or PAL_COLOR_REVERSE
RETURNS	nothing
DESCRIPTION	set the color of the pixel located a column x, row y
REQUIRES	PAL_init() must have been called
EXAMPLE	PAL_setPixel(10, 20, PAL_COLOR_REVERSE) ;

draw a line

 

PROTOTYPE	void PAL_line(char x0, char y0, char x1, char y1, unsigned char mode)
PARAMETERS	x0, y0 : column and row of the start of the line x1, y1 : column and row of the end of the line mode : pixel color, either PAL_COLOR_BLACK,  PAL_COLOR_WHITE or PAL_COLOR_REVERSE
RETURNS	nothing
DESCRIPTION	draw a line from (x0, y0) to (x1, y1)
REQUIRES	PAL_init() must have been called
EXAMPLE	PAL_line(0, 0, 127, 127, PAL_COLOR_WHITE) ;

DRAW A CIRCLE

 

PROTOTYPE	void PAL_circle(char x, char y, char r, unsigned char mode)
PARAMETERS	x : column of the center of the circle y : row of the center of the circle r : radius of the circle mode : pixel color, either PAL_COLOR_BLACK,  PAL_COLOR_WHITE or PAL_COLOR_REVERSE
RETURNS	nothing
DESCRIPTION	draw a circle of radius r centered at (x, y)
REQUIRES	PAL_init() must have been called
EXAMPLE	PAL_circle(30, 30, 5, PAL_COLOR_WHITE) ;

DRAW A SOLID BOX

 

PROTOTYPE	void PAL_box(char x0, char y0, char x1, char y1, unsigned char mode)
PARAMETERS	x0, y0 : top left of the box x1, y1 : bottom right of the box mode : pixel color, either PAL_COLOR_BLACK,  PAL_COLOR_WHITE or PAL_COLOR_REVERSE
RETURNS	nothing
DESCRIPTION	fill a rectangle from corner (x0, y0) to corner (x1, y1)
REQUIRES	PAL_init() must have been called
EXAMPLE	PAL_box(10, 10, 30, 30, PAL_COLOR_WHITE) ;

draw a rectangle

 

PROTOTYPE	void PAL_rectangle(char x0, char y0, char x1, char y1, unsigned char pcolor)
PARAMETERS	x0, y0 : top left of the rectangle x1, y1 : bottom right of the rectangle mode : pixel color, either PAL_COLOR_BLACK,  PAL_COLOR_WHITE or PAL_COLOR_REVERSE
RETURNS	nothing
DESCRIPTION	draw a rectangle from corner (x0, y0) to corner (x1, y1)
REQUIRES	PAL_init() must have been called
EXAMPLE	PAL_rectangle(10, 10, 30, 30, PAL_COLOR_WHITE) ;

draw a character

 

PROTOTYPE	void  PAL_char(unsigned char x, unsigned char y, unsigned char c, unsigned char size)
PARAMETERS	x : pixel column of the top left position of the character, from 0 to 127 y : pixel row of the character, from 0 to number of vertical pixels c : ASCII code of the char size : high nibble is height multiplier, low nibble is width multiplier predefined sizes : PAL_CHAR_STANDARD, PAL_CHAR_DWIDTH, PAL_CHAR_DHEIGHT, PAL_CHAR_DSIZE
RETURNS	nothing
DESCRIPTION	draw char c at (x, y), always in white on black (use PAL_box() to reverse video)
REQUIRES	PAL_init() must have been called
EXAMPLE	PAL_char(3, 5, ‘A’, PAL_CHAR_DSIZE) ;

DRAW A STRING

 

PROTOTYPE	void  PAL_write(unsigned char lig, unsigned char col, unsigned char *s, unsigned char size)
PARAMETERS	lig : text line of the string col : text column of the string s : pointer to the string (NULL terminated) size : high nibble is height multiplier, low nibble is width multiplier predefined sizes : PAL_CHAR_STANDARD, PAL_CHAR_DWIDTH, PAL_CHAR_DHEIGHT, PAL_CHAR_DSIZE
RETURNS	nothing
DESCRIPTION	write string s at position (lig, col)
REQUIRES	PAL_init() must have been called
EXAMPLE	PAL_write(0, 5, myString, PAL_CHAR_STANDARD) ;

DRAW a CONSTANT STRING

 

PROTOTYPE	void  PAL_constWrite(unsigned char lig, unsigned char col, const unsigned char *s, unsigned char size)
PARAMETERS	lig : text line of the string col : text column of the string s : pointer to the constant string (NULL terminated) size : high nibble is height multiplier, low nibble is width multiplier predefined sizes : PAL_CHAR_STANDARD, PAL_CHAR_DWIDTH, PAL_CHAR_DHEIGHT, PAL_CHAR_DSIZE
RETURNS	nothing
DESCRIPTION	same as PAL_write(), but s is a string located in ROM
REQUIRES	PAL_init() must have been called
EXAMPLE	PAL_write(0, 5, myConstantString, PAL_CHAR_STANDARD) ;

DRAW A PICTURE

 

PROTOTYPE	void    PAL_picture(unsigned char x, unsigned char y, const unsigned char *bm, unsigned char sx, unsigned char sy)
PARAMETERS	x : top left pixel column of the picture y : top left pixel row of the picture bm : pointer to a bitmap picture in ROM sx : width of the picture sy : height of the picture
RETURNS	nothing
DESCRIPTION	draw the picture pointed to by bm at position (x, y) bitmap is arranged as a monochrome bitmap, use mikroElektronika GLCD bitmap editor and select T6963 to convert bitmap into source code
REQUIRES	PAL_init() must have been called
EXAMPLE	PAL_picture(0, 0, pict, 128, 128) ;

VIDEO ROUTINE

 

PROTOTYPE	void    PAL_ISR()
PARAMETERS	none
RETURNS	nothing
DESCRIPTION	this function must not be called directly by user, but must be placed within the interrupt() function.Warning : other interrupts may cause bad video synchronization if they are enabled.
REQUIRES	PAL_init() must have been called
EXAMPLE	void    interrupt(void) { PAL_ISR() ; }

The core of the circuit is a PIC18F4620 :

C1, C3 and C4 are decoupling capacitors

The PIC is clocked with a 8 Mhz crystal

D1 is used as temperature sensor connected to PIC ADC

Video signal is mixed through R8 and R9

Switches with pull-downs are used for settings

You can connect the video out signal directly to the composite video input of your TV.

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