snowsh
Well-known member
I am working on a project to replace a z80 based controller board on a large studio mixing console.
I have a fully functioning replacement using an arduino mega2560 rev 3. Now I move to building a production board and I want to use a teensy 4.1. apart from the speed and memory gains, the main thing for me is the native usb midi.
I read a post here where paul stoffregen says it is ok to use 74hct245 octal bus tranceivers to bridge the 3.3v logic lines to 5v. The original z80 board from the 80s uses 245 chips to act a bus buffers and a direction switch on the data bus - perfect. I have made a schematic and pcb layout based on these concepts and I get to wondering if I have all bases covered before I go and order some PCBs.
In my circuit, I use 3 74HCT245 to connect my address. data and system bus lines to the console (exactly as the z80 was). the Z80 was on a Eurocard which slots neatly into a 10 way backpane. I found the correct connector and a kicad template for eurocard.
The eurocard allows connection to other boards via 8bit data bus and related address / control lines. I am yet to fully explore this. It uses 2x 7hHC688 comparators on the address lines, and another 74HCT245 for the databus.
The eurocard also provides 5v power from the console. Nice clean power - so I am definitely using that. I will obviously cut the trace on the 4.1 to isolate the USB power.
I am a bit confused on whether I should step down using the teensys 3.3v pin to power the rest of the voltage lines on my new card, or leave everything powered at 5v. Paul talked about using these 245 chips - and I cant find the post anymore.
So can I stick to 5v on the board for my circuit - will this be OK for the teensy 4.1 pins? they are only connected to to these chips, or to headers to go off to switch panels and displays via ribbon cables with power for the displays and switches.
Here is my schematic:
View attachment schematic for pjrc forum.pdf.
I have a fully functioning replacement using an arduino mega2560 rev 3. Now I move to building a production board and I want to use a teensy 4.1. apart from the speed and memory gains, the main thing for me is the native usb midi.
I read a post here where paul stoffregen says it is ok to use 74hct245 octal bus tranceivers to bridge the 3.3v logic lines to 5v. The original z80 board from the 80s uses 245 chips to act a bus buffers and a direction switch on the data bus - perfect. I have made a schematic and pcb layout based on these concepts and I get to wondering if I have all bases covered before I go and order some PCBs.
In my circuit, I use 3 74HCT245 to connect my address. data and system bus lines to the console (exactly as the z80 was). the Z80 was on a Eurocard which slots neatly into a 10 way backpane. I found the correct connector and a kicad template for eurocard.
The eurocard allows connection to other boards via 8bit data bus and related address / control lines. I am yet to fully explore this. It uses 2x 7hHC688 comparators on the address lines, and another 74HCT245 for the databus.
The eurocard also provides 5v power from the console. Nice clean power - so I am definitely using that. I will obviously cut the trace on the 4.1 to isolate the USB power.
I am a bit confused on whether I should step down using the teensys 3.3v pin to power the rest of the voltage lines on my new card, or leave everything powered at 5v. Paul talked about using these 245 chips - and I cant find the post anymore.
So can I stick to 5v on the board for my circuit - will this be OK for the teensy 4.1 pins? they are only connected to to these chips, or to headers to go off to switch panels and displays via ribbon cables with power for the displays and switches.
Here is my schematic:
View attachment schematic for pjrc forum.pdf.
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