Features:
- 8-port serial UART expansion board for the Raspberry Pi3 (and 2...).
- Stack 4 boards for a maximum of 32 (plus TX0/RX0) serial ports on one RasPi.
- Based on the NXP SC16IS752 DUART chip, 4 per board. 24MHz (or 24.576MHz) master osc.
- Pi-3 "HAT" shaped board, but without the HAT-ID chip.
- Extra header to bring out the Pi's native TX0/RX0 pins.
- Selectable SPI host interface (SPI0, SPI1...).
- Aux 5V input, and on-board 3.3V regulator.
- DC fan output (standard 5V PC fan w/PWM+TACH).
- The host I/F pins are easily jumpered to default pins, or reassigned if necessary.
- TTL-serial I/O on 2x17 headers. The pinout (8 wires per group) is compatible with my other interface paddle boards, YASC2, YASC6, YASC8, YASC485 and YASC485D and YASCDMXRJ4.
You COULD use this board with the previous 26-pin Pi header interface, but a few critical signals may not be a quick 2-pin jumper. That's what wire jumpers (or wire-wrap wire!) are for.
Update 14-Oct-2018: Built the first prototype! I'm ready to test out functionality. Initially, I'll just fly-wire this board over to an Arduino DUE, only because I have no RasPi software skills... so this will be a reasonable alternative.
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Update 16-Sep-2018: After a long hiatus, I finally finished this board and sent it off for fab. I have a friend interested in driving many DMX serial ports with a Pi, so that was my motivation for wrapping up the hardware at last. It's actually a good thing I waited, because I found a lot of tweaks were necessary compared the 1st version from a year ago.
In order to drive the DMX (lighting) control links, the baud rate needs to be 250K (or 500K), so a 24MHz master oscillator divides down nicely for that purpose. It can also serve up a good range of "standard" uart baud rates with a small timing error. If you want perfect "standard" baud rates, you could easily substitute a 24.576MHz master oscillator.
The DMX physical interface for the initial application will be provided by a "YASCDMXRJ4" interface board... which I've also finished (and sent to fab!). It merely provides 4 independant "RS485" ports, pushed out over RJ45 connectors, in the commonly accepted pinout for "DMX-over-UTP". For each 8upPiShield, you would need 2 of the YASCDMXRJ4 interface boards. The cabling is like a standard 34-pin "floppy drive" style ribbon cable.
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