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The CPU Fails to Start When the Long Serial Cable Hangs in the Air

Publication Date:  2015-06-19 Views:  188 Downloads:  0

Issue Description

Hardware configuration:
A 19 m long serial cable between the server and the PC


The server cannot be powered on.

Handling Process

Ensure that the serial cable does not hang in the air.

Root Cause

The serial cable hanging in the air serves as an antenna which interferes with signals received by the CPU. The CPU supposes that data transmission starts and receives incorrect data.

If the serial cable is not connected to the PC and hangs in the air, signals at the transmit data (TXD) end are coupled into the receive data (RXD) end of the serial port. In this case, the CPU receives incorrect signals which are like an incorrect command through the serial port during startup. As a result, the CPU cannot start up, and the MM910 cannot issue a command for powering on the compute node.