I have board with 4 AVR processors. They are communicating over SPI (1 x master AVR M162 + 3 x slave AVR M168) For programming I am using STK 500 - ISP. When I want load program into one cpu, remain cpu are by DIP SWITCH in reset. Some time when I programming one CPU, programs in others are deleted. SPI is 5cm long. Are require some resistors (pull up / down), terminators... ?