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Caravel Rev 5B eval board: J6 (oscillator enable) & J2 (UART EN) label incorrect, misleading #108

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algofoogle opened this issue Jun 24, 2024 · 0 comments

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@algofoogle
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algofoogle commented Jun 24, 2024

Caravel Rev 5B eval/development board found in hardware/development/caravel-dev-v5-M.2 has an incorrect/misleading label on J6 (and somewhat misleading on J2), it seems.

Here's J6:

J6 with label 'OSC /EN'

The label (EN-bar) implies that this is an active-low-ENABLE, and hence that jumpering J6 -- i.e. pulling pin 1 (OSC_EN) low -- would enable the oscillator. In fact, it will do the opposite: The datasheet for part DSC6001 (ref X1) confirms that this an active-low-DISABLE (and when left floating it is pulled high to ENABLE).

DSC6001 datasheet

I reckon the circuit is correct, and just the label is wrong, i.e. it's designed this way so that the on-board oscillator can be disabled and an external clock source can be supplied to xclk via header pin J11[19].

On-board oscillator schematic

Should the label be OSC /DIS (bar over DIS) perhaps, since the intended use of this jumper is really to disable the oscillator?

NOTE: Looks like a similar confusing label with J2:

J2: UART /EN

Maybe this should be labelled UART DIS (no bar) because shorting J2 will pull it HIGH and disable the UART, but it's tricky since the actual pin (pin 2) of this jumper is, in fact, the actual /UART_EN line.

@algofoogle algofoogle changed the title Caravel Rev 5B eval board: J6 (oscillator enable) label incorrect, misleading Caravel Rev 5B eval board: J6 (oscillator enable) & J2 (UART EN) label incorrect, misleading Jun 24, 2024
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