USB AVR Programmer as Programme AND UART


about two month I use the pololu USB AVR Programmer (Win7, WinXPpro, AVRStudio4): a very great thing, very fast and the nice DSO ggg. AND - absolut fine: the thin, long USB-cable.


  1. Using ISP and uart - both connected
    uart GND, TXD and RXD connected, nothing else
  2. different boards, controler usually mega1284
  3. flashing or read signature is not possible
  4. Programmer board becom very hot !

Aktual problem - question:
Is ist NOT possible to have both cables simultaneously with the board? Is it necessary to connect EITHER ISP OR uart? (allwas change the cables - is soo unhandy !)

Many thanks for any answer and best greetings from bavarian mountains/germany

I connect both the UART and programmer cables to the same target board, at the same time, without problems, but you obviously can’t use both functions at the same time.

I suspect there is a problem with the way you have made the power connections, very likely a grounding problem. You may have damaged the programmer and/or the controller. It would help if you post a diagram showing ALL the connections between the PC, power supply, target and programmer boards.

Hello Jim
thanks for your answer.

JR> … may have damaged programmer and/or … controller

Hmmmm. With only one cable at the same time works ISP very good, after disconnecting the ISP cable from the programmer and connecting the uart cable with my board, the uart works good. So I think I have nothing damaged (hope so ! !).

My connections in three different modes are:

notebook (ONLY battery driven)
 +-> USB AVR Programmer
      +-> ISP (with MOSI, MISO, SCK, GND, Vcc, /RES) -> controller

Result: good.

notebook (ONLY battery driven)
 +-> USB AVR Programmer
      +-> UART
           +-> RX   )
           |        )
           +-> TX   } -> controller
           |        )
           +-> GND  )

Result: good.

notebook (ONLY battery driven)
 +-> USB AVR Programmer
      +-> ISP (MOSI, MISO, SCK, GND, Vcc, /RES) -> controller
      +-> UART
           +-> RX  )
           |       } -> controller
           +-> TX  )
           NO GND! because GND is connected on ISP
           but tested also with GND

Result: uart good, ISP gives a reset to the controller and AVRStudio shows the [ISP Mode Error]-window “A problem occurred when …”.

The uart is usually not connectet over GND but I tested the connection with or without GND - with the same bad results. The multimeter show on my controler board 4,89 V with no, one or both connections with the programmer, the [STK500 in ISP mode…] window in AVRStudio 4 show 4.3V with only ISP connected and 4.1 V with the two connections.

How is the controller being powered?


I am sorry you are having trouble with the Pololu USB AVR Programmer. After a failed programming attempt, the programmer’s red error LED should turn on. This means there was an error programming. To see the error details, please run the Pololu USB AVR Programmer Configuration Utility. It should say something informative in the “Error From Last Programming” section. Please take a screenshot of the utility and post it here; you can use the “Upload attachment” tab while composing your reply.

You should definitely be able to connect both the ISP pins and the UART pins at the same time. The fact that the programmer is getting hot and that AVR Studio is reporting a low voltage makes me think that there is a short circuit. To find the problem, we should work on simplifying your system.

  1. You said you were seeing the problem with different target boards. Please select the simplest target board and only use that one.

  2. Please connect the ISP cable alone (without the UART) and try programming again, just to make sure that still works.

  3. Please do some experiments to find the minimal set of UART wires that need to be connected to exhibit the problem. If you only connect the programmers TX to the boards RX, are you still able to program? If you only connect the programmer’s RX to the board’s TX, are you still able to program?

While you are doing this, please avoid letting the programmer become hot for a prolonged period of time because that could damage it.

Once you have the simplest possible system that exhibits the problem, please post a schematic of the system that shows all the connections, details about the target board, and some pictures of your setup.

You should also use your multimeter to check for shorts. For example, is the target board’s RX line shorted to its GND? Is the programmer’s RX pin shorted to the programmer’s GND?


Hello David,

thanks for your description and explanation. The good news: failure: no, (now) all is running well.

First I made the test on a breadboard with a separate controller, same ext. crystal osc. 20 MHz, with minimmum of peripherie etc - and the programmer was running well (ISP and UART). So I was shure, the programmer works right.

Same work with the complex board:

The USB AVR Programmer Configuration Utility shows

Minimum Allowed 4192 mV
Maximum Range Allowed 992 mV

Measurements From Last Programming
Minimum: 2944 mV

Error From Last Programming:
Target VDD either went too low or had too much range, so programming was aborted. Make sure that the target is powered on and its batteries are not too low (if applicable).

Then “big” control of the “bad” board.

fault: remarkable consumption of power from peripheral parts. These parts where connected to the controllers circuit “for tests ohnly” - and not disconnected :frowning:

After connecting the high consumption parts with their own power supply - as designed - the problem was solved.

Many thanks to david, thanks to all.

Sorry for my bad expressions:

"… Then “big” control of the “bad” board …“
mean " … Then “big” check/examination …”

I am glad you were able to solve your problem, and thanks for letting us know what it was. --David