Consul
Well-known member
This forum needs some activity.
I have a couple of SID chips, and I'm hunting around for a couple more. My goal is to make a SID-based polysynth using an FPGA. I have a Nexys2 board with a Xilinx FPGA (1.2-million gate-equivalent - what that means is hard to explain, but you can mostly think of it as exactly what it says) which uses 3.3V power and logic. The SID chips need 5V. Hence, question number one.
I do know that level shifters exist and are out there, but the best ones for my application are all very small (smaller than SOIC) surface mount packages that I'm not equipped to deal with. There's a way to do it with an FET per line, but I keep running into confusion about the spec of FET I need to make that work. I don't think I need bidirectional shifting, so I'm wondering if simple op amp circuits with appropriate voltage gain, as well as some current gain, would work.
That actually brings me to a design conundrum. For a polysynth, I could drive all four SIDs with the same set of address and data lines (5 address, 8 data) so that they all have the same settings at any one time. For a basic polysynth, this is fine, and thirteen amplifiers with enough current gain to drive all the loads wouldn't be so hard. But if I want to add a solo mode, that would mean that I'd want to be able to send separate settings to each chip, which would then all fire at once from a single note on. So that means four 8-bit data buses and a 5-bit address bus (they can all still share that one), for a total of 37 amplifiers. That seems like a lot of work.
My second question is to do with MIDI and optoisolators. The first thing I plan to get working is processing MIDI in. I understand the spec just fine (it's simpler than RS232, really), but I'm wondering how the optoisolator works. Does it have its own power rails, or can I just treat it like a passive component?
Thank you all for the help! After taking a digital design class using FPGAs and VHDL, I've finally gotten excited about electronics again.
I have a couple of SID chips, and I'm hunting around for a couple more. My goal is to make a SID-based polysynth using an FPGA. I have a Nexys2 board with a Xilinx FPGA (1.2-million gate-equivalent - what that means is hard to explain, but you can mostly think of it as exactly what it says) which uses 3.3V power and logic. The SID chips need 5V. Hence, question number one.
I do know that level shifters exist and are out there, but the best ones for my application are all very small (smaller than SOIC) surface mount packages that I'm not equipped to deal with. There's a way to do it with an FET per line, but I keep running into confusion about the spec of FET I need to make that work. I don't think I need bidirectional shifting, so I'm wondering if simple op amp circuits with appropriate voltage gain, as well as some current gain, would work.
That actually brings me to a design conundrum. For a polysynth, I could drive all four SIDs with the same set of address and data lines (5 address, 8 data) so that they all have the same settings at any one time. For a basic polysynth, this is fine, and thirteen amplifiers with enough current gain to drive all the loads wouldn't be so hard. But if I want to add a solo mode, that would mean that I'd want to be able to send separate settings to each chip, which would then all fire at once from a single note on. So that means four 8-bit data buses and a 5-bit address bus (they can all still share that one), for a total of 37 amplifiers. That seems like a lot of work.
My second question is to do with MIDI and optoisolators. The first thing I plan to get working is processing MIDI in. I understand the spec just fine (it's simpler than RS232, really), but I'm wondering how the optoisolator works. Does it have its own power rails, or can I just treat it like a passive component?
Thank you all for the help! After taking a digital design class using FPGAs and VHDL, I've finally gotten excited about electronics again.