Displaying and scrolling large amount of text on 8x14 led dot matrix display?

[CuriousOne]

Hello!

I'm building a custom stereo spectrum analyzer for home system. It will have 8x14 led dot matrix display. Having such nice display inspired me to use it for showing additional data, such as name of input selected, show volume level while adjusting and so on. The problem is that EPROM space of chip I want to use PIC16F887 is quite limited, so having whole font in memory is not possible.

My approach is as follows:

1. Attach an external eeprom chip, where letter graphics and other symbols will be stored
2. create a lookup table, so we know that say data for "B" starts at address F940 and data for "X" starts say at FFCD.
3. Alocate a virtual "frame buffer" in chip eeprom, which will be read by separate routine in interrupt, which will update the display.
4. As needed, transfer data from external eeprom to internal.

The question is, to have smooth display, I will need to update it at least 30 times per second. Reading internal eeprom so much times will cause it to fail quite fast, I guess? The possible workaround is to use SRAM chip, but maybe I'm making things too complicated and there are simpler ways to solve it? I don't want to use external IC like MAX7219 or similar, I want to do everything purely my MCU powers.

[Art]

For 8x14 bits it’s far from unreasonable to store the frame buffer in the pic’s RAM as 14 bytes.
It may take time to write from EEPROM to the frame buffer in RAM, but at least when it comes time
to update the display frame, that can be fast so you don’t see the display being drawn.

[richard]

a 14x8 font would be nicely accommodated in a pic16's flash pgm memory (its 14 bits wide) if you have the space

[CuriousOne]

14x8 is the display dimensions. Actual "font" and graphics will be smaller, say 5x8.

[Dave]

CouriousOne, the question:" I will need to update it at least 30 times per second. Reading internal eeprom so much times will cause it to fail quite fast, I guess? " NO reading the eeprom from the particular processor will not wear it out BUT, Writing to the same locations of PROGRAM MEMORY more than 1000 or so times will. Also writing to internal EEPROM MEMORY more than 100,000 times will.

[Art]

A 5x8 font with uppercase characters, digits and basic punctuation is 472 bytes,
but if you only need to use several words and omit characters you don’t need,
it may fit on the 256 bytes on chip EEPROM, or a combination of on-chip EEPROM and program memory.

Here is the 5x8 font used by the hitachi LCD controllers (if the forum fits it in the post)
It’s in a C array, but the data is the same.

You’ll notice the bottom value is always zero because the character display is actually only 5x7,
so that’s a decent head start

unsigned char charmap[472]={
	0b00000, // Space _ 0x20
	0b00000,
	0b00000,
	0b00000,
	0b00000,
	0b00000,
	0b00000,
	0b00000, //
	0b00100, // Exclamation ! 0x21
	0b00100,
	0b00100,
	0b00100,
	0b00000,
	0b00000,
	0b00100,
	0b00000, //
	0b01010, // Inverted Commas " 0x22
	0b01010,
	0b01010,
	0b00000,
	0b00000,
	0b00000,
	0b00000,
	0b00000, //
	0b01010, // Hash # 0x23
	0b01010,
	0b11111,
	0b01010,
	0b11111,
	0b01010,
	0b01010,
	0b00000, //
	0b00100, // Dollar Sign $ 0x24
	0b01111,
	0b10100,
	0b01110,
	0b00101,
	0b11110,
	0b00100,
	0b00000, //
	0b11000, // Percent Sign % 0x25
	0b11001,
	0b00010,
	0b00100,
	0b01000,
	0b10011,
	0b00011,
	0b00000, //
	0b01100, // And Sign & 0x26
	0b10010,
	0b10100,
	0b01000,
	0b10101,
	0b10010,
	0b01101,
	0b00000, //
	0b01100, // Inverted Comma ' 0x27
	0b00100,
	0b01000,
	0b00000,
	0b00000,
	0b00000,
	0b00000,
	0b00000, //
	0b00010, // Open Bracket ( 0x28
	0b00100,
	0b01000,
	0b01000,
	0b01000,
	0b00100,
	0b00010,
	0b00000, //
	0b01000, // Close Bracket ) 0x29
	0b00100,
	0b00010,
	0b00010,
	0b00010,
	0b00100,
	0b01000,
	0b00000, //
	0b00000, // Asterisk * 0x2A
	0b00100,
	0b10101,
	0b01110,
	0b10101,
	0b00100,
	0b00000,
	0b00000, //
	0b00000, // Plus Sign + 0x2B
	0b00100,
	0b00100,
	0b11111,
	0b00100,
	0b00100,
	0b00000,
	0b00000, // Comma , 0x2C
	0b00000,
	0b00000,
	0b00000,
	0b00000,
	0b01100,
	0b00100,
	0b01000,
	0b00000, //
	0b00000, // Dash/Minus Sign - 0x2D
	0b00000,
	0b00000,
	0b11111,
	0b00000,
	0b00000,
	0b00000,
	0b00000, //
	0b00000, // Period/Decimal Point . 0x2E
	0b00000,
	0b00000,
	0b00000,
	0b00000,
	0b01100,
	0b01100,
	0b00000, //
	0b00000, // Forward Slash / 0x2F
	0b00001,
	0b00010,
	0b00100,
	0b01000,
	0b10000,
	0b00000,
	0b00000, //
	0b01110, // 0 0x30
	0b10001,
	0b10011,
	0b10101,
	0b11001,
	0b10001,
	0b01110,
	0b00000, //
	0b00100, // 1 0x31
	0b01100,
	0b00100,
	0b00100,
	0b00100,
	0b00100,
	0b01110,
	0b00000, //
	0b01110, // 2 0x32
	0b10001,
	0b00001,
	0b00010,
	0b00100,
	0b01000,
	0b11111,
	0b00000, //
	0b11111, // 3 0x33
	0b00010,
	0b00100,
	0b00010,
	0b00001,
	0b10001,
	0b01110,
	0b00000, //
	0b00010, // 4 0x34
	0b00110,
	0b01010,
	0b10010,
	0b11111,
	0b00010,
	0b00010,
	0b00000, //
	0b11111, // 5 0x35
	0b10000,
	0b11110,
	0b00001,
	0b00001,
	0b10001,
	0b01110,
	0b00000, //
	0b00110, // 6 0x36
	0b01000,
	0b10000,
	0b11110,
	0b10001,
	0b10001,
	0b01110,
	0b00000, //
	0b11111, // 7 0x37
	0b00001,
	0b00010,
	0b00100,
	0b01000,
	0b01000,
	0b01000,
	0b00000, //
	0b01110, // 8 0x38
	0b10001,
	0b10001,
	0b01110,
	0b10001,
	0b10001,
	0b01110,
	0b00000, //
	0b01110, // 9 0x39
	0b10001,
	0b10001,
	0b01111,
	0b00001,
	0b00010,
	0b01100,
	0b00000, //
	0b00000, // Colon : 0x3A
	0b01100,
	0b01100,
	0b00000,
	0b01100,
	0b01100,
	0b00000,
	0b00000, //
	0b00000, // Semi Colon ; 0x3B
	0b01100,
	0b01100,
	0b00000,
	0b01100,
	0b00100,
	0b01000,
	0b00000, //
	0b00010, // Less Than Sign < 0x3C
	0b00100,
	0b01000,
	0b10000,
	0b01000,
	0b00100,
	0b00010,
	0b00000, //
	0b00000, // Equals Sign = 0x3D
	0b00000,
	0b11111,
	0b00000,
	0b11111,
	0b00000,
	0b00000,
	0b00000, //
	0b01000, // Greater Than Sign > 0x3E
	0b00100,
	0b00010,
	0b00001,
	0b00010,
	0b00100,
	0b01000,
	0b00000, //
	0b01110, // Question Mark ? 0x3F
	0b10001,
	0b00001,
	0b00010,
	0b00100,
	0b00000,
	0b00100,
	0b00000, //
	0b01110, // Ampersand @ 0x40
	0b10001,
	0b00001,
	0b01101,
	0b10101,
	0b10101,
	0b01110,
	0b00000, //
	0b01110, // A 0x41
	0b10001,
	0b10001,
	0b10001,
	0b11111,
	0b10001,
	0b10001,
	0b00000, //
	0b11110, // B 0x42
	0b10001,
	0b10001,
	0b11111,
	0b10001,
	0b10001,
	0b11110,
	0b00000, //
	0b01110, // C 0x43
	0b10001,
	0b10000,
	0b10000,
	0b10000,
	0b10001,
	0b01110,
	0b00000, //
	0b11100, // D 0x44
	0b10010,
	0b10001,
	0b10001,
	0b10001,
	0b10010,
	0b11100,
	0b00000, //
	0b11111, // E 0x45
	0b10000,
	0b10000,
	0b11110,
	0b10000,
	0b10000,
	0b11111,
	0b00000, //
	0b11111, // F 0x46
	0b10000,
	0b10000,
	0b11110,
	0b10000,
	0b10000,
	0b10000,
	0b00000, //
	0b01110, // G 0x47
	0b10001,
	0b10000,
	0b10111,
	0b10001,
	0b10001,
	0b01111,
	0b00000, //
	0b10001, // H 0x48
	0b10001,
	0b10001,
	0b11111,
	0b10001,
	0b10001,
	0b10001,
	0b00000, //
	0b01110, // I 0x49
	0b00100,
	0b00100,
	0b00100,
	0b00100,
	0b00100,
	0b01110,
	0b00000, //
	0b00111, // J 0x4A
	0b00010,
	0b00010,
	0b00010,
	0b00010,
	0b10010,
	0b01100,
	0b00000, //
	0b10001, // K 0x4B
	0b10010,
	0b10100,
	0b11000,
	0b10100,
	0b10010,
	0b10001,
	0b00000, //
	0b10000, // L 0x4C
	0b10000,
	0b10000,
	0b10000,
	0b10000,
	0b10000,
	0b11111,
	0b00000, //
	0b10001, // M 0x4D
	0b11011,
	0b10101,
	0b10101,
	0b10001,
	0b10001,
	0b10001,
	0b00000, //
	0b10001, // N 0x4E
	0b10001,
	0b11001,
	0b10101,
	0b10011,
	0b10001,
	0b10001,
	0b00000, //
	0b01110, // O 0x4F
	0b10001,
	0b10001,
	0b10001,
	0b10001,
	0b10001,
	0b01110,
	0b00000, //
	0b11110, // P 0x50
	0b10001,
	0b10001,
	0b11110,
	0b10000,
	0b10000,
	0b10000,
	0b00000, //
	0b01110, // Q 0x51
	0b10001,
	0b10001,
	0b10001,
	0b10101,
	0b10010,
	0b01101,
	0b00000, //
	0b11110, // R 0x52
	0b10001,
	0b10001,
	0b11110,
	0b10100,
	0b10010,
	0b10001,
	0b00000, //
	0b01111, // S 0x53
	0b10000,
	0b10000,
	0b01110,
	0b00001,
	0b00001,
	0b11110,
	0b00000, //
	0b11111, // T 0x54
	0b00100,
	0b00100,
	0b00100,
	0b00100,
	0b00100,
	0b00100,
	0b00000, //
	0b10001, // U 0x55
	0b10001,
	0b10001,
	0b10001,
	0b10001,
	0b10001,
	0b01110,
	0b00000, //
	0b10001, // V 0x56
	0b10001,
	0b10001,
	0b10001,
	0b10001,
	0b01110,
	0b00100,
	0b00000, //
	0b10001, // W 0x57
	0b10001,
	0b10001,
	0b10101,
	0b10101,
	0b10101,
	0b01010,
	0b00000, //
	0b10001, // X 0x58
	0b10001,
	0b01010,
	0b00100,
	0b01010,
	0b10001,
	0b10001,
	0b00000, //
	0b10001, // Y 0x59
	0b10001,
	0b10001,
	0b01010,
	0b00100,
	0b00100,
	0b00100,
	0b00000, //
	0b11111, // Z 0x5A
	0b00001,
	0b00010,
	0b00100,
	0b01000,
	0b10000,
	0b11111,
	0b00000,};
//