Thursday, July 13, 2017

Z8410 DMA chip for the ZX Spectrum Next

So the ZX Spectrum Next team have added a Z80 DMA chip, the Z8410  chip to be more precise. This was popular add on in Europe ( more info here: ), and has some very cool advantages for future games, especially because it's now a standard part. However information on it is a little thin on the ground, so after some major googling, I've found the info on them.

The DMA port can be 11 or 107, and it can transfer around 865k per second
From the web page above: Max. speed of data transfer on ZX128+ is...

17.3 kB(17727 bytes) / frame = 865.6 kB(886350 bytes) / second.

Or.... 1 byte every 4 T-States.

Now here is the really cool bit, because it's tied to the clock speed, when you speed up the NEXT (as it can go 7Mhz, 14Mhz and 28Mhz), the DMA will also speed up!  This is amazing, as it means you'll be able to transfer 1.73Mb/s, 3.46Mb/s, and an astounding 6.92Mb/s!  At 28Mhz you won't be using Layer 2, and that means you could copy the original Layer 1 screen in just 13.5 scanlines, which is incredible.

The registers are below, and here is the Datasheet


mikele said...

Thank you for interesting stuff here.
I'm playing a bit with DMA (using ZXBasic + NextBuild). Is there a possibility to use transfer method which takes into account a transparent color?
Kind regards,

thomas said...

Now that the Next is getting close to completion, I'm warming up my old Spectrum programming skills - thanks for all the information and code examples you are providing here and in the CSpect package! This is very cool.