Graphics RAM
The Graphics RAM (GRAM) is an 8-bit RAM unit of 512 bytes mapped into the Intellivision memory map from $3800-$39FF. Programs may load custom graphics into the Graphics RAM memory and have the STIC render the graphics to the display for either the background or MOBs.
Because the Graphics RAM is attached to the STIC's private graphics bus, the CPU can only access it during VBlank Period 2.
This article describes how pictures are encoded in graphics memory (both GRAM and GROM).