I'm not sure if my question is exactly related but, I'll ask it here.

As I was able to get running 144x32 pixels ST7920 LCD module (Physically and comand-wise compatible with Hitachi HD44780 based 1602 LCD displays) with simple LCDOUT statements (no ASM, hard to guess commands and so on). Now I'm developing an "upgrade" code, which will use this display module with my own charset. Due to relatively high pixel density (144x32 vs 80x16 on HD44780), it is possible to display 18 chars X 4 lines text with 8x8 font on this module. These modules have built-in fonts (about 8192 characters!) but they're either big or ugly. So own character library is a must.

So my idea is as follows (I already started coding it, and so far it appears to be going in the right direction).

Use external EEPROM like 24C32, to hold graphic data for 128 characters, 8x8 pixels each.
Develop a code, which reads appropriate character from external EEPROM and sends it to display according to user specified position.
The main issue is that you can't that simply update specified location of this display module. Updates always are done in 16 bit increments - space for 2 chars. So when writing say character to position #3, I should take care about what is shown at position #4, and actually re-draw it, along with position #3. For this I plan to have array consisting of 72 elements (18x4), which will be updated and looked up before sending data to display, to avoid the character loss.
There will be some other routines too, for reading and sending data to display. I estimate that all this will use about 2KB of code memory. But what about RAM? PBP manual says, arrays are limited to 96 bytes on PIC16 series. I guess this is related to amount of free ram. And if my array uses 72 bytes, will be there ram left for other my code? I mean, the code might compile to 2-3kb, but there will be no RAM to run additional code. Is such situation possible?

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