5 ms·

I am not an electrical engineer so can someone explain how this thing can just piggyback on the existing chip like that. Is the existing cpu still doing things

by aidos 8y ago

I am not an electrical engineer so can someone explain how this thing can just piggyback on the existing chip like that. Is the existing cpu still doing things and this can read additional instructions the other one doesn’t see?

jacobush 8y ago
All other Amiga "accelerators" from back in the day, tell, (by setting a pin low or high or something) the original CPU to stay quiet and off.
armitron 8y ago
If you're talking about the A600 version that sits on top of the original 68k, it's disabled and never used for anything.
snvzz 8y ago
AIUI, at least Vampire V500v2, the one I have and for absurd reasons to do with physical distance with my Amigas haven't been able to test despite a year passed, 68k is removed and Vampire put in its place.
paulmd 8y ago
Usually the way these boards work is to simply pull all the CPU pins out to a separate socket. Apple called their equivalent the "Processor Direct Slot" and I'd assume the Amiga works in the same way. https://en.wikipedia.org/wiki/Processor_Direct_Slot https://en.wikipedia.org/wiki/Processor_Direct_Slot You can typically pull some lines down and the CPU will stop clocking, or the accelerator card can follow the CPU clock and bang data directly into it. It provides very low-level and direct control of the CPU.
- jacobush 8y ago
  Some Amiga CPUs were socketed, some were soldered. Some accelerator boards replaced the slotted CPU, most just deactivated the stock CPU.
rpiguy 8y ago
This is called piggy-backing and it has several uses. Early PCs would stack/piggy-back memory chips to increase capacity. This was possible because of how memory was addressed. Another use is to find dead chips. If you put a working chip on top of a dead chip it will read the signals and work. Finally, in the case of the Vampire and other accelerators for PLCC socketed chips, the accelerator hi-jacks the bus telling the original CPU to do nothing while it takes over the bus. Electrically there is no trickery, think of each pin as plugging two cords into a power strip. Both get power even though there is one source. This probably would not work with modern chip packaging and modern frequencies, but it was a common technique back in the day.
zerohp 8y ago
Unexpanded Amiga 500/600/1200 don't use the 68000's DMA support, so an accelerator board can ground the bus request line and take over the system bus.
reaperducer 8y ago
Another example of piggybacking is the Commodore 64's (and one model of PETs') 6581 SID sound chip. Back in the 80's you could bend a couple of the legs out of a second 6581, solder it to the first one, add a couple of wires (and maybe a diode? Can't quite remember), and now you had two sound chips for stereo sound. These days for some reason people who choose to mod 64's make it unnecessarily complicated with tiny daughterboards and all kinds of needless circuitry. (They also learn how to do it from YouTube videos. We did it from ASCII text files!)
rasz 8y ago
original chip is disabled, its IO buffers put in Hi-Z (high impedance) mode. 386/486 PC motherboards did the same thing when you used coprocessor/upgraded soldered CPU using socket.

by aidos 8y ago

jacobush 8y ago

All other Amiga "accelerators" from back in the day, tell, (by setting a pin low or high or something) the original CPU to stay quiet and off.

armitron 8y ago

If you're talking about the A600 version that sits on top of the original 68k, it's disabled and never used for anything.

snvzz 8y ago

AIUI, at least Vampire V500v2, the one I have and for absurd reasons to do with physical distance with my Amigas haven't been able to test despite a year passed, 68k is removed and Vampire put in its place.

paulmd 8y ago

Usually the way these boards work is to simply pull all the CPU pins out to a separate socket. Apple called their equivalent the "Processor Direct Slot" and I'd assume the Amiga works in the same way. https://en.wikipedia.org/wiki/Processor_Direct_Slot https://en.wikipedia.org/wiki/Processor_Direct_Slot You can typically pull some lines down and the CPU will stop clocking, or the accelerator card can follow the CPU clock and bang data directly into it. It provides very low-level and direct control of the CPU.

jacobush 8y ago
Some Amiga CPUs were socketed, some were soldered. Some accelerator boards replaced the slotted CPU, most just deactivated the stock CPU.

rpiguy 8y ago

This is called piggy-backing and it has several uses. Early PCs would stack/piggy-back memory chips to increase capacity. This was possible because of how memory was addressed. Another use is to find dead chips. If you put a working chip on top of a dead chip it will read the signals and work. Finally, in the case of the Vampire and other accelerators for PLCC socketed chips, the accelerator hi-jacks the bus telling the original CPU to do nothing while it takes over the bus. Electrically there is no trickery, think of each pin as plugging two cords into a power strip. Both get power even though there is one source. This probably would not work with modern chip packaging and modern frequencies, but it was a common technique back in the day.

zerohp 8y ago

Unexpanded Amiga 500/600/1200 don't use the 68000's DMA support, so an accelerator board can ground the bus request line and take over the system bus.

reaperducer 8y ago

Another example of piggybacking is the Commodore 64's (and one model of PETs') 6581 SID sound chip. Back in the 80's you could bend a couple of the legs out of a second 6581, solder it to the first one, add a couple of wires (and maybe a diode? Can't quite remember), and now you had two sound chips for stereo sound. These days for some reason people who choose to mod 64's make it unnecessarily complicated with tiny daughterboards and all kinds of needless circuitry. (They also learn how to do it from YouTube videos. We did it from ASCII text files!)

rasz 8y ago

original chip is disabled, its IO buffers put in Hi-Z (high impedance) mode. 386/486 PC motherboards did the same thing when you used coprocessor/upgraded soldered CPU using socket.