BUS PWR JP4 JP5 HOW-TO

USB AVR Programmer and SPI interface. Adafruit's USBtinyISP.

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wtfwtfdef
 
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BUS PWR JP4 JP5 HOW-TO

Post by wtfwtfdef »

I cut the trace and placed the unplaced jumper here, so its active like it is normally, but i can deactivate it with a jumper. I am wondering what it does? I see from the schematic that it takes Vcc and connects it to pin4 of the usb?? I've searched the forums thoroughly and can find no mention of bus pwr or jp4 or what it does? Can someone please explain to me the purposes of jp4 and jp5 and how to utilize these features? I understand jp5 is a self program, why exactly would you need this? To reprogram the usptinyisp if a new firmware was released? How would I do this? Any help would be greatly appreciated, thank you.

I have a feeling that jp4 may just be VCC ? Im puzzled by this, afaik jp3 is supposed to provide power?

Also what are the reasons for jumpering R4 and R7? How come the 1.5Kohm wont be good enough to drive other chips for programming? Why is the MOSI and CLK loads going to be too heavy? Is it because it is limiting current to those lines? Can someone show what calculations prove this? If these Resistors are jumpered are they then going to cause problems programming small things or the spokepov?

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adafruit_support_rick
 
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Re: BUS PWR JP4 JP5 HOW-TO

Post by adafruit_support_rick »

That jumper is an obsolete artifact of an earlier design. It does the exact same thing as JP3 - it connects USB 5V power to the target through ICSP pin 2.

R4 and R7 should be installed when programming a SpokePOV. If the target device already has resistors on MOSI and SCK, then these resistors may limit the current too much for successful programming, and they should be replaced by jumpers.

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phild13
 
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Re: BUS PWR JP4 JP5 HOW-TO

Post by phild13 »

From the FAQ on the USBtinyISP:
What is "Self Program"?

The original USBtinyISP could be programmed by another programmer by jumpering a pin. This is not true anymore now that there is a buffer. You should ignore the jumper.

Also, you cannot program the usbtiny with itself.

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adafruit_support_rick
 
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Re: BUS PWR JP4 JP5 HOW-TO

Post by adafruit_support_rick »

Actually, self-program is yet another unused jumper. I'm not certain what J4 was for originally.

wtfwtfdef
 
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Re: BUS PWR JP4 JP5 HOW-TO

Post by wtfwtfdef »

Thanks for the replies. Are they any examples of chips that have resistors on them? Or is this for in-circuit programming like the tube-clock? I'll take a look at the schematic for the tube clock. I've programmed attiny2313's and attiny85's and atmega8's without problem with the resistors in place, but then again they were just the chips, not in-circuit, so I knew there was no external resistance, and the chip datasheets say nothing of internal resistances. Are there any chips that it will give problems for ? or is this mainly an in-circuit requirement?

EDIT:

But if i disconnect the jumper, then the tinyisp itself gets no power from the USB? In the board layout files the pin is always connected via the through hole, so without the bottom trace, which i cut, and i jumper it, it operates as normal. if i disconnect the jumper then I've removed power to VCC. It seems it needs this jumper for the usbtinyisp to function, not to program power to the chip being programmed. I dont understand why the jumper would be left. In design is it easier to just have made that pin a through-hole and connected top+bottom? Why not remove the jumper pad, save the money/time from silkscreening/drilling thse holes?

So to clarify now that I put this jumper there, how am I going to remove 5V from the board I want to progarm if it has its own power?

Rick: so you are saying that I have to remove both pins now to power the chip being programmed?

Another Q is : Can you remove/open the jumpers while its running? or does this require a plug-replug?

I guess I'll have to do some experimenting, i'll report back.

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adafruit_support_rick
 
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Re: BUS PWR JP4 JP5 HOW-TO

Post by adafruit_support_rick »

If you cut the trace, then you need to jumper it to pass USB power to the rest of the USBtiny.

The idea is not that the chips have resistors, it's that you're programming a chip in-circuit, and the circuit puts loads on the pins.

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phild13
 
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Re: BUS PWR JP4 JP5 HOW-TO

Post by phild13 »

JP4 and JP3 are connected together. One on one end of the circuit board and the other on the other end.

The purpose of JP4 is USB bus power (+5v) from the USB cable. It is permanently connected by a pc board trace and its purpose is to supply power from the USB cable to power the USBtiny circuit board.

The USB cable through JP4 (USB Bus Power) will also power the device (processor) that is being programmed and depending upon circuit design, try to power (which it may not be able to do) the rest of the circuit the device is connected to if and only if the jumper JP3 is connected. This is very handy if your programming 5v chips out of circuit, like on a breadboard.

If JP3 (called USB power) is not connected then no +5v power can reach the device from the USBtiny and the device will have to be externally powered. The USBtiny will still be powered by the USB cable through JP4.

The idea is by removing the jumper from JP3 you isolate the +5v from the device being programmed. The USBtiny will self-power (through JP4) but buffer the I/O to match the target device. This means you can program 3.3v devices. The circuit the 3.3v device is in must be powered.

Leaving the jumper JP3 connected when programming a device powered 5v chip will not hurt anything.
Leaving JP3 connected when programming a 3.3v chip will damage the 3.3 volt chip by applying 5v to it.

Most of the time I leave the JP3 jumper connected even if the +5v device is powered by the circuit it is in. It does not seem to hurt anything.

Tip
Unplug the USBtiny USB cable from the computer usb port. and connect the desired ribbon cable to the device to be programmed. Power the device if it is still in circuit and then plug the USB cable into the computer. Windows drivers seems to like it better this way and will recognize the USBtiny easier.
Don't forget to remove the JP3 jumper if the device is 3.3v before powering anything up.

Tip:
Icetube clock
Remove the tube from the clock, connect the 6 pin ribbon cable properly and then power the clock from the wall wart. With the tube still in the clock it does some strange things during programming and generally programming will fail.

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