The Master System comes from a long line of succession. What started as a collection of off-the-shelf components, has now gained a new identity thanks to Sega’s engineering.
A very detailed look at Sega’s first international console, the Master System.
Having 8KBytes of internal RAM, but mirrored (which means that the bit A13 isn’t being decoded), means that they could have used Memory Mapped IO for the VDP, and gain a little bit of speed, because the IO instructions are slightly slower than memory ones.
I don’t think so, the memory is local to the VDP, and only accessible via ports on the VDP (like the TI chip it’s based on). Putting the memory on the bus would’ve meant difficult bus-arbitration between the main bus and the bus between the VDP and the gfx memory.
It’s a nice enough summary, but he did goof on the vram interface – it’s not 16 bit. It has 8 bits for reading data from the DRAM, and 8 bits for combined address out and writing data to the DRAM. It was designed for one bit DRAM chips with separate data in/out lines. If you read through the VDP manual, it’s pretty clear as they show how you wire the VDP to DRAM chips.
I see the guy accepts contributions, why don’t you open an issue at his repo? We don’t know if he will read this
Good idea. I left an issue on his github repo. Thanks for bringing that up.
This was a fun read. I’ve built a number of Z80 based machines including a Colecovision clone, and its amazing how much can be done with such simple hardware.
Thank you for sharing!