I am trying to understand which pins I can use to supply power to the XK-1A board - I am struggling to understand the schematic diagram I am looking at on p13 of the Hardware Manual, in particular the use of 5VSK and 5VHD, the difference between which is a bit unclear to me, and VCC4V3 which the diagram seems to imply (rather paradoxically) is wired direct to 5VSK.
Anyway, in my design I have a nominal 5V supply from a USB-to-UART cable which I would like to use to drive the board. The natural place to feed this in is on the IOB expansion pins that the UART is connected to, and this seems to work, but I'm not certain (1) whether this is exactly equivalent to passing it through the 5VIN plug on the board, and (2) if what I am doing bypasses one level of voltage regulation then whether that is a problem or not.
It would certainly be more convenient to go over IOB, but I'd appreciate any advice on whether this is a good idea or not!
XK-1A 5v supply
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jmtaylor
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Bianco
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The power supply of the XK-1A works as follows:
When exclusively powered by the plug (male pins, where the XTAG2 sticks into), the mosfet TR2 will be closed and will feed the regulators and also connected to the supply pins at the socket (female pins).
When exclusively powered by the DC jack, the supply pin of the DC jack will feed the regulators and also connected to the supply pins at the socket (female pins)
When powered by both the plug and DC jack the mosfet will be open and the board will be supplied by the DC jack (see above).
These are the normal operating conditions.
You can supply the board by plug, socket or DC jack.
If you supply it with the socket, it is better to leave the supplies of the jack and plug unconnected.
When exclusively powered by the plug (male pins, where the XTAG2 sticks into), the mosfet TR2 will be closed and will feed the regulators and also connected to the supply pins at the socket (female pins).
When exclusively powered by the DC jack, the supply pin of the DC jack will feed the regulators and also connected to the supply pins at the socket (female pins)
When powered by both the plug and DC jack the mosfet will be open and the board will be supplied by the DC jack (see above).
These are the normal operating conditions.
You can supply the board by plug, socket or DC jack.
If you supply it with the socket, it is better to leave the supplies of the jack and plug unconnected.
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jmtaylor
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Thanks very much for your detailed reply, that is very helpful. Things make more sense now that I recognise 5VSK as connected to the JTAG "socket" and 5VHD to the JTAG pin "header".
Am I correct in reading from the diagram on p13 that 5VSK and VCC4V3 are directly connected to one another? That would imply that supplying a voltage on pin 15 of IOA is exactly equivalent to supplying it on pin 1 of JTAGOUT (which I think is your final case "If you supply it with the socket"). It makes construction easier if I can supply over IOA since I need to wire those connectors up anyway.
Am I correct in reading from the diagram on p13 that 5VSK and VCC4V3 are directly connected to one another? That would imply that supplying a voltage on pin 15 of IOA is exactly equivalent to supplying it on pin 1 of JTAGOUT (which I think is your final case "If you supply it with the socket"). It makes construction easier if I can supply over IOA since I need to wire those connectors up anyway.
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Bianco
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Yup the 5VSK and VCC4V3 are the same net with two names.
Care must be taken however to avoid shorting two power supplies when you connect the XTAG2 debug adapter since this will always feed the board if there is no DC plug in the DC jack
Care must be taken however to avoid shorting two power supplies when you connect the XTAG2 debug adapter since this will always feed the board if there is no DC plug in the DC jack