Former ASM coder from HP48

The Saturn architecture is nibble-based; that is, the core unit of data is 4-bit-sized, which can hold one binary-coded decimal (BCD) digit.

The Saturn microprocessor is a hybrid 64-bit / 20-bit CPU hardware-wise but acts like a 4-bit processor in that it presents nibble-based data to programs and uses a nibble-based addressing system.

The screen is 34 X 4-bit memory sized width (like 136 pixels) but only 131 real hardware pixel width displayed.

1 Like

So are the other 5 pixels are overscan or not actually wired up?

overscan, you have to move your pointer to 34 “4-bits” nibbles to go ahead to the next line of 131 pixels :slight_smile:

1 Like

Unless the pixels are organised as bytes representing vertical columns, so that the screen buffer can just be blasted to it, conversion could be tricky and/or screen updates would be very slow.

No you can’t because games are written in Machine language that is so specific to Saturn Hp48’s Micro controller. You can easily copy bitmaps into a new Ardu’s project though, just like Diamonds game.

I was thinking of the artwork itself.- of course they are 4 greyscalvao will need reworking anyway but it’s a lot less than starting from scratch.

1 Like

4 shade of grey bitmaps are composed with two consecutive monochrome bitmaps, so it’s pretty easy to port.
Also keep in mind that 80% of all HP49 games were made in monochrome :slight_smile:

1 Like

Is that an exact 80% or a statistic made up on the spot? :grinning:

1 Like

The main reason I like the HP48 is because of Chip-48 (the extended version of Chip-8).

Statistic on the spot :slight_smile:)
Actually full greyscale games were rare, or at least just the splash screen were made using greyscales