LPC54608 eva board ISP,SDRAM pin

[実奥山]

CPU packege is 180-pin, TFBGA  in OM13092 board

C8 pin is connected to SDRAM and ISP switch.

There is a 2.2K resistor(R108) between the ISP switch and the CPU.

Why are you using a 2.2K resistor?

Shouldn't it be a 0 ohm resistor?

[carstengroen]

My guess would be to protect the CPU if the ISP switch is pressed while the pin is used for accessing SDRAM. The 2.2K resistor will limit the current if switch is pressed during SDRAM access, at the same time its value is low enough to pull the pin low during boot (and activate ISP)