hi friends, I am Using 5 (C8051F120) MicroControllers in My Project with the following settings. SPI Mode: Multi Master Mode - 4 wire Clock rate : 2.4 Mhz clock phase bit: 0 Clock polarity bit: 0 Weak pull up: Enabled 4 MCUs uses its own GPIO pins to select the 5th MCUs's NSS. The GPIO Pin of the 4 MCUs are Shorted to the NSS pin of the 5th MCU.At this time i Face the Following Problem 1 among the 4 MCUs select the 5th MCU by pulling its GPIO pin low. But at the same time, other 3 MCUs pull the same NSS pin pin high. At this time , the NSS pin of the 5th MCU is not getting low. The GPIO pins are configured as open drain. Any one know how to solve the problem?