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System to Share a Single RS-232 Serial Port Between Multiple Blade Servers

IP.com Disclosure Number: IPCOM000125920D
Original Publication Date: 2005-Jun-22
Included in the Prior Art Database: 2005-Jun-22
Document File: 2 page(s) / 29K

Publishing Venue

IBM

Abstract

In BladeCenter systems there is a need to support a real serial port for serial console output. Today's implementation incorporates a serial connector for every blade forcing a user to manually connect to each blade in order to get access to the console. An external serial multiplexer could be used to connect to each blade simultaneously but, the equipment is costly and creates cable routing problems. Serial Over LAN is another solution but, it requires network connectivity. A solution is required that provides real serial port access to multiple blade servers in a convenient manner. This article describes how to multiplex multiple systems' RS-232 ports to a single connector using a shared bus structure. Only one system will have access to the external port through the shared bus at any time. Since only one cable exits the box, the solution is low cost and reduces rack cabling problems for the BladeCenter chassis. In comparison to a simple multiplexing structure, the shared bus structure reduces connector cost and wiring complexity for the midplane.

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System to Share a Single RS-232 Serial Port Between Multiple Blade Servers

    In BladeCenter systems there is a need to support a real serial port for serial console output. Today's implementation incorporates a serial connector for every blade forcing a user to manually connect to each blade in order to get access to the console. An external serial multiplexer could be used to connect to each blade simultaneously, but the equipment is costly and creates cable routing problems. Serial Over LAN is another solution, but it requires network connectivity. A solution is required that provides real serial port access to multiple blade servers in a convenient manner. This article describes how to multiplex multiple systems' RS-232 ports to a single connector using a shared bus structure. Only one system will have access to the external port through the shared bus at any time. Since only one cable exits the box, the solution is low cost and reduces rack cabling problems for the BladeCenter chassis. In comparison to a simple multiplexing structure, the shared bus structure reduces connector cost and wiring complexity for the midplane.

    The system consists of three major components: a blade transmitter/receiver, a chassis transmitter/receiver, a shared serial bus, and a Transmit/Receive selector.

    The blade transmitter/receiver resides on each blade and is responsible for converting the TTL/CMOS signaling from the Serial port to a line level suitable for a high speed multidrop environment. The RTS/CTS handshake lines are also converted to a suitable bus signaling level. The line drivers must be capable of disabling its outputs and inputs so that only one blade is transmitting or receiving on the shared bus at any one time. The transceiver must not cause errors on the shared bus when being inserted and removed from the chassis. The serial lines entering the blade serial port are biased in such a way as to not cause errors when the blade's transceiver is disabled.

    The chassis transceiver resides i...