Abstract:
The present invention includes a multi-mode SCSI backplane and a detection logic that is used in conjunction with the backplane. In this invention, the SCSI backplane can be configured in different modes, included simplex mode and duplex mode. The detection logic can also detect when an illegal configuration is connected to the SCSI backplane and indicate the presence of the illegal configuration by triggering a light emitting diode (LED) or some other indicating mechanism. The detection logic is implemented with a handful of cost-effective field effect transistors (FETs), resistors and LEDs and no additional IC logic gates or Programmable Array Logic (PAL) is necessary.

Description:
CROSS REFERENCE TO RELATED PATENTS 
   The SCSI backplane of the present invention is related to the subject matter disclosed in U.S. Pat. No. 6,055,582, issued on Apr. 25, 2000 for: “SCSI Duplex-Ready Backplane for Selectively Enabling SCSI Simplex and Duplex Modes Based on Indication of Desired SCSI Mode” assigned to Compaq Computer Corporation, Houston, Tex., the disclosure of which is herein specifically incorporated in its entirety by this reference. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates, in general, to a multi-mode SCSI backplane, and to configuration logic that detects whether the SCSI backplane is configured for simplex or duplex mode, and also detects illegal cabling configurations. 
   2. Relevant Background. 
   The SCSI (small computer system interface) connection interface provides a fast, versatile way for PCs and servers to connect with a variety of storage devices including hard disk drives (HDDs), optical drives, and tape drives, among others. A common configuration for SCSI interfaces in servers includes a SCSI circuit board known as a backplane that typically includes SCSI connectors. In a typical configuration, the SCSI backplane is internal to a server box, and interfaces with the main motherboard of the server via a cabled SCSI connection. The SCSI controller circuitry is typically located on the server motherboard, the SCSI backplane, or both boards. 
   Multi-mode SCSI backplanes are designed to support multiple connection configurations including simplex mode configuration and duplex mode configuration. While multi-mode SCSI backplanes have the advantage of supporting multiple configuration modes on a single SCSI backplane, they also have added expense and design complications. For example, multi-mode SCSI backplanes typically have to incorporate complex logic such as Programmable Array Logic (PALs) in the backplane. Furthermore, multi-mode SCSI backplanes often use sideband signals through additional connector interfaces external to the SCSI interface. 
   Another problem occurs when an operator incorrectly attempts to connect peripheral devices to the SCSI backplane. These so called illegal configurations include illegal cabling configurations and improper termination of connectors that are not in use, among other errors. Illegal configurations can cause the SCSI interface to malfunction and may even result in permanent circuit damage. 
   SUMMARY OF THE INVENTION 
   The present invention includes a configuration logic circuitry for a multi-mode SCSI backplane comprising a SCSI connector coupled to the SCSI backplane, a fault output coupled to the first SCSI connector, and a mode output coupled to the first SCSI connector. 
   The present invention also includes a multi-mode SCSI backplane that includes configuration logic circuitry, said backplane comprising a SCSI connector that includes a first, second and third connector contact, wherein the first connector contact is coupled to a first gate of a first transistor, and said first transistor is also coupled to a mode output and the second connector contact, the second connector contact is coupled to a second gate of a second transistor, and said second transistor is also coupled to a fault output and a ground, and the third connector contact is coupled to a third gate of a third transistor, and said third transistor is also coupled to the fault output. 
   These and other features and advantages of the invention, as well as the structure and operations of various embodiments of the invention, are described in detail below with reference to the accompanying figures. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a diagram for the detection logic used with the multi-mode SCSI backplane of the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings above, and will herein be described in detail. It should be understood, however, that the drawings and detailed description thereto are not intended to limit the invention to the particular form disclosed, but on the contrary, the intention is to cover all modifications, equivalents and alternatives falling within the spirit and scope of the present invention as defined by the appended claims. 
   The multi-mode SCSI detection logic of the present invention can be used to detect and indicate several configuration modes in a multi-mode SCSI backplane including a simplex configuration mode, a duplex configuration mode, and illegal configurations that may cause the SCSI backplane to malfunction. When the SCSI backplane is in simplex mode, the SCSI backplane supports a single SCSI bus. In duplex mode, the SCSI backplane includes two SCSI buses where each bus can support the same number of peripherals or a different number of peripherals. 
   Turning now to  FIG. 1 , a diagram of the detection logic  100  used with the SCSI backplane is shown. In this example, the logic  100  includes three SCSI connectors  102 ,  140  and  170 , which for identification purposes are individually referred to as SCSI connector A  102 , SCSI connector B  140 , and SCSI connector C  170 , and which can connect to peripherals, controllers, terminators, jumpers, or other circuitry. The SCSI connectors  102 ,  140 , and  170  are standard 68-contact SCSI connectors, though other types of SCSI connectors, such as 50-contact and 80-contact SCSI connectors, can also be used. 
   The fault output  190  and the mode output  192  are coupled to all three SCSI connectors  102 ,  140  and  170 . In this example, when the voltage level goes low on the fault output  190 , a light emitting diode, or some other kind of indicator, is triggered to indicate that the logic  100  is detecting an illegal configuration. Similarly, when the voltage level goes low on the mode output  192 , a light emitting diode, or some other kind of indicator, is triggered to indicate that the logic  100  detects that the SCSI backplane is in simplex mode. Other signaling conventions are contemplated by the present invention, such as indicating an illegal configuration when the voltage goes high on the fault output  190  and indicating the SCSI backplane is in simplex mode when the voltage goes high on the mode output  192 . 
   In this example, three contacts on each of the SCSI connectors  102 ,  140  and  170  are coupled to the rest on the logic  100 . Starting with SCSI connector A  102 , a first A contact  104  of the connector  102  remains unconnected. The second A contact  106  is connected to the source side of transistor  112 , while the drain side is coupled to line  118  which, in turn, is coupled to the fault output  190 . The gate of transistor  112  is coupled to a power supply  114  that keeps the voltage on the gate high, typically about +5 volts, thereby keeping the transistor  112  open and allowing an electronic coupling of the second A contact  106  to line  118  and the fault output  190 . 
   The third A contact  108  of SCSI connector  102  is coupled to the source side of transistor  110 . The drain side of transistor  110  is coupled to line  118 , while the gate of the transistor  110  is coupled to the third B contact  146  of SCSI connector  140 . The gate of transistor  110  is also coupled via resistor  117  to ground  116  which normally keeps the voltage on the gate low, thereby keeping transistor  110  closed. 
   Turning now to SCSI connector B  140 , the first B contact  142  is coupled to the gate of transistor  156  and ground  154  via resistor  153 . The ground  154 , which is also coupled to the gate of transistor  156  via resistor  153 , normally keeps the gate at low voltage which, in turn, keeps the transistor  156  closed. The second B contact  144  is connected to the gate of transistor  148  and the source of transistor  156 . The gate of transistor  148  is also connected to power supply  150  via resistor  149  that normally keeps the transistor  148  open and pulls line  118  low. As mentioned in the discussion of the SCSI connector A  102 , the third B contact  146  is coupled to the gate of transistor  110  and ground  116 . 
   Turning now to SCSI connector C  170 , the first C contact  172  is coupled to diode  186  that, in turn is coupled to power supply  188 . The second C contact  174  is coupled to ground  178 . The third C contact  176  is coupled to the gate of transistor  182  and ground  180  via resistor  179 . The gate of transistor  182  is also coupled to ground  180  via transistor  179 , thus normally keeping the gate at low voltage and transistor  182  closed. When transistor  182  is closed, the ground  184  is not electronically coupled to line  118  and fault output  190 . 
   In this example, a fault signal power supply  120  is coupled via resistor  119  to the fault output  190  through line  118  and a mode signal power supply  158  is coupled via resistor  157  to the mode output  192  through line  160 . Both of these power supplies  120  and  150  normally keep high (typically about +5 Volts) the applied voltage on the fault output  190  and mode output  192 . 
   All the transistors shown in this example are standard, n-type Field Effect Transistors (FETs), but the present invention contemplates examples where only p-type FETs are used as well as combinations of n-type and p-type FETs. Furthermore, the present invention contemplates using other types of switches and gates to control the path of signals in the logic  100 . 
   An example of a multi-mode SCSI backplane based on the detection logic shown in  FIG. 1  may be a dual SCSI bus backplane with a first SCSI bus originating at SCSI connector A  102  and ending at SCSI connector B  140 , and a second SCSI bus that originates at SCSI connector C  170  and ends with terminators on the SCSI backplane. In one example, the first SCSI bus may be a 2-drive SCSI bus and the second SCSI bus may be a 4-drive SCSI bus. In this example, when the SCSI backplane is configured in simplex mode a jumper cable is connected between SCSI connectors B and C,  140  and  170 , to join the first and second SCSI buses into a single, 6-drive SCSI bus that originates at SCSI connector A  102  and ends with terminators on the SCSI backplane that are coupled to SCSI connector C  170 . When the SCSI backplane is configured in duplex mode a terminator board is connected to SCSI connector B  140  that terminates the first SCSI bus originating on SCSI connector A  102  and ending with the terminator board. Meanwhile, the second SCSI bus originates on SCSI connector C  170  and ends with terminators on the SCSI backplane. 
   In this example of the multi-mode SCSI backplane, GEM LED logic may support all the peripherals connected to the single, 6-drive SCSI bus when the SCSI backplane is in simplex mode. In addition, the GEM LED logic may support one of the two SCSI buses present when the SCSI backplane is in duplex mode. In duplex mode, the GEM LED logic may support the second, 4-drive SCSI bus and the first, 2-drive SCSI bus is not supported. The invention also contemplates additional GEM LED logic on the SCSI backplane for support of both SCSI buses when the SCSI backplane is in duplex mode. 
   Using the example shown in  FIG. 1 , the SCSI backplane can be configured for simplex mode by connecting SCSI connector B  140  and SCSI connector C  170  together with a jumper cable (not shown). Peripherals (not shown) may connect to the simplex configured SCSI backplane via connector A  102 . The jumper cable provides electronic coupling between the first B contact  142  and first C contact  172 , the second B contact  144  and the second C contact  174 , and the third B contact  146  and the third C contact  176 . 
   When the first B contact  142  and first C contact  172  are coupled, power supply  188  drives the voltage higher on the gate of transistor  156 , which causes the transistor  156  to go from a closed to open state. When the second B contact  144  and second C contact  172  are coupled, the ground  178  is coupled to the source side of transistor  156 , which drives the voltage low across the now open transistor  156 , line  160  and mode output  192 . Based on the signaling convention used in this example, the lower voltage at mode output  192  triggers a light emitting diode, or some other kind of indicator (not shown) to indicate that the logic  100  detects that the SCSI backplane is in simplex mode. 
   Connecting the jumper between the SCSI B connector  140  and SCSI C connector  170  couples the third B contact  146  and third C contact  176  which couples the ground  180  to the gate of transistor  110 . The voltage applied to the gate of transistor  110  is normally kept low by ground  116  coupled to resistor  117 , so connecting the gate to an additional ground  180  does not change normally closed state of transistor  110 . 
   When the SCSI connectors B and C  140 ,  170  are jumpered together to put the SCSI backplane in simplex mode, the SCSI connector A  102  provides the connection to the single SCSI bus. The single SCSI bus may be coupled to LED blinking logic, such as Generic Equipment Model (“GEM”) LED logic developed by the Semiconductor Equipment and Materials International (SEMI) standards organization, that provides blinking LED support to a wide variety of peripherals on the SCSI bus. 
   The SCSI backplane can be configured for duplex mode by connecting a terminator board to SCSI connector B  140 . The terminator board includes a first terminator contact that may stay unconnected, a second terminator contact that may be connected to a ground on the terminator board, and a third terminator contact that may be connected to a power supply on the terminator board. These three contacts on the terminator board may be configured such that when the terminator board is connected to SCSI connector B  140 , the first terminator contact may be coupled the first B contact  142 , the second terminator contact may be coupled to the second B contact  144  and the third terminator contact may be coupled to a third B contact  146 . 
   When the terminator board is connected to SCSI connector B  140  as described above, the first B contact  142  is not being driven and is left to be pulled low by ground  154  that is coupled to resistor  153 . This results in the gate of transistor  156  also being at low voltage, opening gate  154 . When the transistor  156  is open, the voltage on line  160  and mode output  192  remains high to signal that the backplane is in duplex mode. 
   When the SCSI backplane in this example is in duplex mode, SCSI connector A  102  provides access to a first duplex SCSI bus, and SCSI connector C  170  provides access to a second duplex SCSI bus. The first duplex SCSI bus supports up to 2 peripherals, while the second duplex SCSI bus supports up to 4 peripherals and includes LED blinking logic, such as GEM LED logic. While the first duplex SCSI bus in this example does not include blinking LED logic, the present invention contemplates modifications that provide such logic to the first duplex SCSI bus. 
   Illegal configurations of peripherals and other circuitry connected to one of the SCSI buses can also be monitored. Illegal configurations can include, for example, a terminator board installed in the wrong SCSI connector, the wrong controller connected to the first SCSI bus when the SCSI backplane is in duplex mode, a missing terminator that results in an unterminated bus, and improper termination of a peripheral. When an illegal configuration is detected, the voltage applied to the fault output  190  goes low which triggers a light emitting diode, or some other kind of indicator that the SCSI backplane is configured in an incorrect manner and that a SCSI bus may fail to operate properly. 
   One example of a SCSI configuration that may trigger a fault condition at fault output  190  is when a terminator board is improperly installed on SCSI connector A  102  while the SCSI backplane is configured in simplex mode. With the terminator board installed in SCSI connector A  102  the voltage on second A contact  106  will be driven low because the second terminator contact is coupled to a ground. Since the gate of transistor  112  is coupled to power  114 , transistor  112  remains closed. Therefore, the fault output  190  is driven low by the grounding of the second A contact  106 , triggering a fault condition on the SCSI backplane. 
   Another example of a SCSI configuration that may trigger a fault condition at fault output  190  is a jumper cable is improperly installed between SCSI connector A  102  and SCSI connector C  170 . Here, when the jumper cable is installed between the two connectors, the voltage on second A contact  106  is driven low by ground  178  that is coupled to the second C contact  174 . Similar to the example above, the low voltage on the second A contact  106  drops the voltage at the fault output  190 , triggering a fault condition on the SCSI backplane. 
   Another example of a SCSI configuration that may trigger a fault condition at fault output  190  is the connection of a jumper cable improperly installed between SCSI connector A  102  and SCSI connector B  140 . In this configuration, the gate of transistor  148  remains a high voltage, and the transistor  148  remains closed. Ground  152  is able to drive the voltage on fault output  190  low, triggering a fault condition on the SCSI backplane. 
   Another example of a SCSI configuration that may trigger a fault condition at fault output  190  is the connection of a terminator board to SCSI connector A  102  or SCSI connector C  170  while the SCSI backplane is in duplex mode. For example, when a terminator board is connected to SCSI connector C  170 , the third C contact  176 , is coupled to power on the third terminator contact. The high voltage on third C contact  176  results in high voltage on the gate of transistor  182 , closing the transistor and driving the fault output  190  low due to the ground  184 . The low voltage on the fault output  190  triggers a fault condition on the SCSI backplane. 
   In another example of a SCSI configuration that may trigger a fault condition, a PCI controller is connected to SCSI connector A  102  while the SCSI backplane is in duplex mode. In this example, the PCI controller has a first PCI contact connected to power, a second PCI contact that is not connected, and a third PCI contact that is connected to a ground. When the PCI controller is connected to SCSI connector A  102 , the first PCI contact is coupled to the first A contact  104 , the second PCI contact is coupled to the second A contact  106 , and the third PCI contact is coupled to the third A contact  108 . When the third A contact  106  is coupled to the third PCI contact, the voltage on the third A contact  108  is driven low due to the third PCI contact being connect to a ground. As a result, the voltage across transistor  110  goes low, and also pulls down the voltage of line  118  and the fault output  190 , triggering a fault condition on the SCSI backplane. 
   One example of the present invention has the SCSI connectors  102 ,  140  and  170  shown in  FIG. 1  as 68-contact SCSI connectors that have connector contact assignments in conformity with the SCSI Parallel Interface-2 (SPI-2) standard and locates first contacts A, B and C  104 ,  142  and  172 , respectively, at connector contact # 52 ; second contacts A, B and C  106 ,  144  and  174 , respectively, at connector contact # 19  and third connector A, B and C  108 ,  146  and  176 , respectively, at connector contact # 20 . 
   Although the invention has been described and illustrated with a certain degree of particularity, it is understood that the present disclosure has been made only by way of example, and that numerous changes in the combination and arrangement of parts can be resorted to by those skilled in the art without departing from the spirit and scope of the invention, as hereinafter claimed.