Hopefully TK can give a diffinitive answer to this question…
If a MIDI IO module is connected to a STM32F4 core via J11E what is the voltage level of the MIDI out signal on the MIDI IO module?
The discription of the jumpers on the PCB on the STM32F4 core page indicates that it’s 3v. Is this correct or is the MIDI Out signal 5v?
i measure 4 you :
@J11 Core 5v between VS and 4,1V Pin (should be 5V thenthe pcb is already labeld with +5V,)
between VS and MI1-4 i measure 3Vs (should 3,3 maybe - my displays consume much…)
between VS and MO1-4 i measure 0,5V
@a midiport which is sending > has on my board 3,9VDC which i assume should be 5V - so 5V then!
i use an application which uses 2xMIO Boards
Hi Rowan,
this is a typo in the documentation: 3.3V outputs are only available for MBHP_CORE_LPC17 due to a chip limitation (erratum).
MBHP_CORE_STM32 and MBHP_CORE_STM32F4 configure the output pins in open drain mode, which means that the pin is in high impedance state if no MIDI message or a logic-1 is sent. Via the 220 Ohm resistors and the optocoupler at the receiver side, the voltage level will be pulled to ca. 4..5V.
The MBHP_MIDI_IO board has an additional 100k pull-up resistor to 5V, but this one is only used to ensure a proper signal for the LED indicators.
Best Regards, Thorsten.
Told yah
Cool, Thanks. That clears that up then.