# Shared programming pins

Alright so there is a question that I need to ask. I am designing a PCB and I plan to include a ISP header for programming. Now one of the programming pins (PB3 - MOSI) is connected to a push button which I take input from. According to the application note (AVR042) I need to connect a 330ohm resistor between the button and the pin. I wanted to ask if it will cause any problem with the button input or not. Also, is my reset connected correctly?

EDIT: The labels are not correctly showing up in EAGLE, my pin config is as follows:

PB3- MOSI

PB4- MISO

PB5 - SCK

PC6 - RESET


Also, the jumper JP_SPST connects to the buttons.

• If you are concerned, why don't you connect the push button to a different pin? You have for example PD7 available. Also, why do you ask about the RESET line? – nickagian Jul 25 '17 at 10:48
• That would add unnecessary complications to the code I wrote if I moved on button to another port. My intuition tells me that it should be fine even without the resistor as long as the switch is open. About the reset line, I wanted to ask if the programmer will pull it down correctly due to the connected resistor. – hacker804 Jul 25 '17 at 10:57
• @hacker804: your diagramm doesn't show where the ISP Header pins are connected to. They are just labeled (MOSI, RESET, SCK, MISO). Do you really expect us to look up where those lines are on this specific ATMEGA chip? Also: where is the button you are talking about? Please put some minmal effort into your question (including diagram) to make it possible to give a qualified answer. – Curd Jul 25 '17 at 10:59
• Err, I'd think it'd be easier to change the code instead of unnecessarily doubling up pin functionality. GPIO code isn't really too complicated anyways. Code is super easy to change, hardware isn't (I say this as a professional embedded software engineer). – Phyllostachys Jul 25 '17 at 12:47
• For the first question, the 330Ohms resistance on the button pin does not interfere with the programmation and the input voltage detection. As you have a default open button on the MOSI pin, the resistor is optionnal. For the RESET pin, if you don't use external reset signal, you can omit the pull up resistor (R3). – Foxrider83 Jul 25 '17 at 13:11