Following on from my post about the Phoenix freeplay mod http://www.ukvac.com/forum/phoenix-enhanced-freeplay_topic352965.html, I've now managed to get the high score hardware working.
I designed a plug-in replacement circuit board for Phoenix boards, replacing the existing RAM #4000-#43FF with non-volatile RAM. 2 options were designed into the same board, either to use 6116 RAM with battery backup, or use a Dallas NVRAM module (although these modules are getting old now and more difficult to find which is why I also designed in the 6116 option).
There was a problem, though, and it appeared to be speed-related. The old RAM that I needed to replace is made up of a couple of 2114's
rated at 450nS access time. The replacement memory is much quicker than the old (100-200nS), and when I installed it, I got
the occasional corruption to the screen and other memory, eventually
causing the game to crash.
So studying the schematics, it appears the original designers were aware of the potential problem, but the old RAM was just so slow it didn't care. Having a look at the schematics shows the odd capacitor here and there on inputs to gates, especially around the memory addressing area. There was one capacitor shown that wasn't present on my board, so I installed one, and used the slowest RAM I could find in the module. I've now had the game tested for a couple of days and it's performed flawlessly.
It uses the same code I released last week for the free play mod, so there's nothing really different to see in the game although it still supports all the features of the freeplay mod. There isn't a high score table [no ROM space to make one], so all that happens is when you turn the game off, when you turn it back on the high score is still there!
I've a number of spare PCB's that will shortly be for sale in the relevant section on here. You'll need to desolder the existing 2x2114's as they tend not to be socketed, but the Phoenix PCB seems to be quite good quality so I've not had any problems with lifted tracks. You'll also need to install the relevant capacitor if it's not already present, and use as slow a RAM chip as you can find. It seems to work fine with Dallas 200nS modules, and 6116-3 (150nS) but I'd suggest using 6116-4 (200nS) chips if you build that version.
So some photos:-
I designed a plug-in replacement circuit board for Phoenix boards, replacing the existing RAM #4000-#43FF with non-volatile RAM. 2 options were designed into the same board, either to use 6116 RAM with battery backup, or use a Dallas NVRAM module (although these modules are getting old now and more difficult to find which is why I also designed in the 6116 option).
There was a problem, though, and it appeared to be speed-related. The old RAM that I needed to replace is made up of a couple of 2114's
rated at 450nS access time. The replacement memory is much quicker than the old (100-200nS), and when I installed it, I got
the occasional corruption to the screen and other memory, eventually
causing the game to crash.
So studying the schematics, it appears the original designers were aware of the potential problem, but the old RAM was just so slow it didn't care. Having a look at the schematics shows the odd capacitor here and there on inputs to gates, especially around the memory addressing area. There was one capacitor shown that wasn't present on my board, so I installed one, and used the slowest RAM I could find in the module. I've now had the game tested for a couple of days and it's performed flawlessly.
It uses the same code I released last week for the free play mod, so there's nothing really different to see in the game although it still supports all the features of the freeplay mod. There isn't a high score table [no ROM space to make one], so all that happens is when you turn the game off, when you turn it back on the high score is still there!
I've a number of spare PCB's that will shortly be for sale in the relevant section on here. You'll need to desolder the existing 2x2114's as they tend not to be socketed, but the Phoenix PCB seems to be quite good quality so I've not had any problems with lifted tracks. You'll also need to install the relevant capacitor if it's not already present, and use as slow a RAM chip as you can find. It seems to work fine with Dallas 200nS modules, and 6116-3 (150nS) but I'd suggest using 6116-4 (200nS) chips if you build that version.
So some photos:-
