Low impedance loads on ICSP header

Good day!

I plan to program my arduino directly without bootloader via ICSP header. I use pins 10, 11, 12 in my device.

This page: http://arduino.cc/en/Hacking/PinMapping168 says that one should avoid low impedance loads on these pins while programming MCU using ISP.

What are examples of such low impedance loads? I figured out if I have simple LEDs on this pins, the ISP works ok.

What are examples of such low impedance loads? I figured out if I have simple LEDs on this pins, the ISP works ok.

It is warning you that the ICSP programmer to be used may not have the same pin driving capablities that an Arduino has. So it depends on the specific hardware programmer that you will be using. A led may or may not be too much of a load for it.

Lefty

My ISP programmer is an Arduino with ArduinoISP.

Thanks!

I've found an advice to put 10k resistors on ISP lines when using them, for example for 16x2 LCD at the same time, like this:

What is the reason to have this resistors? What they are protecting?

those resistors are preventing the programming signals from being drowned out by whatever is on the other end of the pins.

If you can, you should just avoid using those pins at all. the clock is particularly touchy.

Thanks for the response, one another question -- when using external programmer, should I power it from my device, or device from programmer?

I plan to program my arduino directly without bootloader via ICSP header. I use pins 10, 11, 12 in my device.

My ISP programmer is an Arduino with ArduinoISP.

when using external programmer, should I power it from my device, or device from programmer?

I understand that the programmer is an arduino but it's not clear what the target is. Generally you can power the target any way that works as long as it's 5v - just be sure to connect the grounds.

you might want to describe the setup a bit more.

The target is bare ATmega8A on a breadboard, so it seems the either way works, thanks!

Side question about Arduino ICSP header. Assuming programming Arduino board with external programmer via Arduino's ICSP header. 5V pin in ICSP header is for powering Arduino from programmer or for power programmer from Arduino? Can't figure this out...

5V pin in ICSP header is for powering Arduino from programmer or for power programmer from Arduino? Can't figure this out...

I know that some programmers do NOT power the target circuit, so I assume all don't and that you will need another PSU for the target.

I think the 5v signal is used to test the target's VCC and set the programmer's voltage-level conversion logic if any. The Atmel spec however is a bit ambiguous.

When programming the target microcontroller, the programmer outputs need to stay within the ranges specified in the DC Characteristics. To easily adapt to any target voltage, the programmer can draw all power required from the target system. This is allowed as the In-System Programmer will draw very little power from the target system, typically no more than 20 mA. The programmer shown in this application note operates in this mode. As an alternative, the target system can have its power supplied from the programmer through the same connector used for the communication. This would allow the target to be programmed without applying power to the target externally.

and

VCC, Allow the In-System Programmer to draw power from the target system, to adapt to any allowed target voltage. The maximum current needed to power the programmer will vary depending on the programmer being used.

Every circuit I've seen has the ISP VCC pin connected to the target VCC.

As for the above circuit, it should work unless some application is actively driving MISO, in which case it will override the programmer's signal.

Also, there is a remote chance that the programming signals may affect the other logic on MOSI and SCK.


Rob

Thanks for the reply, it is what I was looking for...