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Emulating a 3.5 MHz Spectrum on a 4 Mhz MTX is rather optimistic and the effective Spectrum clock is roughly 2.4 MHz. The Speculator outputs 1/6th of the display every interrupt to the VDP, therefore display refresh is 50/6 = 8.33 Hz. That's definitely sub-standard but it's the best I could do at th...

Question: Why hasn't anyone produced a modern copy of Speculator? This community is still thirsty for software and the Spectrum has tons. Dave, I know, has a Speculator and so do others here probably. Tony Brewer, the developer, is part of the community and would maybe provide "spiritual guida...

Tony, this is amazing stuff. :o Incredible that after all these years, the Z80 still has unknown corners to explore. Thanks for the reply, Steve. Visual Z80 is an almost perfect simulation (not emulation) of the Z80 and the Remix version is the easiest way to examine those corners. Here is an expla...

New Z80 return to zero discovery yesterday: two combinations of input signals will result in a RET instruction returning to address 0000.

Visual Z80 (VZ80 for short) is an online transistor-level simulation of the Zilog NMOS Z80 CPU. Recently, Visual Z80 Remix (VZ80R for short) was created that uses the VZ80 simulator with a more user-friendly interface: https://floooh.github.io/visualz80remix/ Improvements include Assembler and Timin...

Martin, many thanks for your tests. MTX BASIC might be affecting the results. I ought to write a short assembler program for you to try, however there is no urgent need for this info. My expectation is that parts of sprites on active lines but completely off the display to the left or right will set...

I might not be the only one, but I've not tried anything as I don't really understand the question. Sorry! The aim is to test limits of collision using two sprites with same pattern at same x,y coordinate. Test 1 is extreme left test with one set bit at x = 0-32. Test 2 is extreme right test with o...

I'd like to confirm the range of x coordinates for which the VDP does sprite collision detection. I cannot test this myself in real hardware as my MTX is in the attic. I think the following two extremes will set the sprite collision bit: 1. Use two 8x8 (or 16x16) sprites with same patterns. Pattern ...

To synchronise a Propeller, how about putting /VDPINT on the system bus by soldering a wire (must be yellow) from VDP pin 16 or CTC pin 23 to A25 on J10? This assumes LK12 is missing. The obvious downside of that is that it would stop the board from being "plug & play", most folks who...

The issue is the difference between 50Hz and 60Hz. Games use the VDP interrupt to update the VDP only when it is not refreshing the screen. Since the Propeller is running at a different refresh rate, it frequently draws the screen partly through an update, resulting in display artifacts such as spu...