Abstract:
A communication module includes a switch circuit operable to connect an internal bus to an external bus for, e.g., diagnostics, verification, and fault analysis. The internal bus allows data communication between electronic components internal to the communication module, and the external bus allows data communication between at least one internal electronic component and a device external to the communication module. The switch circuit may be controlled via a programmable and password protected register within the communication module.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    Referring to FIG. 1, a conventional fiber-optic communication module  100 , which may be used in a digital communication system, typically includes a receiver section  101 , a transmitter section  102 , and a controller section  103 , which are all coupled via an internal bus  105 . In some communication modules (not shown), the internal bus is an analog bus. However, because of the many signals to be communicated between the receiver, transmitter and controller, the number of wire traces needed in such an analog bus may become too numerous for practical application. Therefore, the internal bus  105  is a digital bus. In operation, the controller  103  controls and monitors the receiver  101  and transmitter  102  via the bus  105 .  
           [0002]    The communication module  100  also communicates with one or more external devices  120 , via an external bus  115 . Typical external devices  120  include diagnostic devices and configuration devices. The external bus  115  is coupled to the transmitter  102 , (although it may be coupled to the controller  103  or the receiver  101 ). This allows the external device  120  to communicate with the receiver  101 , and controller  103  via the transmitter  102  and bus  105  that act as an interface to the external device  220 .  
           [0003]    The external device  120 , however, does not have direct access to the internal bus  105 , and thus, does not have direct access to the receiver  101  and the controller  103 . And, even though the bus  115  is directly coupled to the transmitter  102 , the external device may be unable to the control the transmitter  102  to the extent that the controller  103  can. Consequently, it is sometimes difficult to externally troubleshoot the communication module  100  because access to the internal bus  105  is often imperative for diagnostics, verification, and fault analysis.  
           [0004]    One solution is to implement an entire separate (from the bus  115 ) bus connection (not shown) for data exchange and communication between an external device and the internal bus  105 , but this may increase the complexity and pinout of the module  100 , and may introduce noise on the bus  105 . Furthermore, it is often difficult to physically probe with the internal bus  105  from the outside of the communication module  100  because the internal bus  105  may be within an intermediate, and thus, inaccessible, layer of a printed circuit board.  
         SUMMARY OF THE INVENTION  
         [0005]    In one aspect of the invention, a communication module includes a switch circuit operable to connect an internal bus to an external bus for, e.g., diagnostics, verification, and fault analysis. The internal bus allows data communication between electronic components internal to the communication module, and the external bus allows data communication between at least one internal electronic component and a device external to the communication module. The switch circuit may be controlled via a programmable and password protected register within the communication module.  
           [0006]    One advantage of a communication module having a diagnostic switch is that by coupling the external bus directly to the internal bus, diagnostics, verification and fault analysis can be performed on the communication module externally. By using the external bus for connection to the internal bus, a separate diagnostics bus is unnecessary, thus, the total number of pins external to the module is reduced. Furthermore, the communication module need not be disassembled during diagnostics, verification, and fault analysis. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]    The foregoing aspects and many of the attendant advantages of this invention will become more readily appreciated as the same become better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein:  
         [0008]    [0008]FIG. 1 is a block diagram of a conventional fiber-optic communication module;  
         [0009]    [0009]FIG. 2 is a block diagram of a fiber-optic communication module according to an embodiment of the invention; and  
         [0010]    [0010]FIG. 3 is a block diagram of a digital communication system that incorporates one or more of the fiber-optic communication modules of FIG. 2 according to an embodiment of the invention. 
     
    
     DETAILED DESCRIPTION  
       [0011]    The following discussion is presented to enable a person skilled in the art to make and use the invention. The general principles described herein may be applied to embodiments and applications other than those detailed below without departing from the spirit and scope of the present invention. The present invention is not intended to be limited to the embodiments shown, but is to be accorded the widest scope consistent with the principles and features disclosed or suggested herein.  
         [0012]    [0012]FIG. 2 is a block diagram of a fiber-optic communication module  200  according to an embodiment of the invention. Like the communication module  100  of FIG. 1, the communication module  200  of FIG. 2 comprises a plurality of internal electronic components including a receiver  201 , a transmitter  202 , and a controller  203 , which are coupled to an internal two-wire serial digital bus  205 . Each of these electronic components may be disposed on a separate integrated circuit or may comprise different areas of a single integrated circuit. Likewise, the internal bus  205  may be disposed within an integrated circuit or may comprise a separate bus structure within the communication module  200 .  
         [0013]    The controller  203  is the bus master for the internal bus  205  and facilitates communications between the other internal electronic components such as the receiver  201  and the transmitter  202 . The internal bus  205  allows data to be read from and written to registers residing in memory and that are referenced by bus addresses within the receiver  201  and the transmitter  202 . For example, the internal bus  205  is coupled to the A3 registers  210  in the receiver  201  and the A4 registers  211  in the transmitter  202 . In one embodiment, there are 256 A3 registers  210  and  256  A4 registers  211 .  
         [0014]    The communication module  200  also coupled to an external bus  215 , which is designed to allow an external device  220  to read from and write to registers that interface the external bus  215  to the internal bus  205  during normal operation of the module  200 . Specifically, the external bus  215  is coupled to the A1 and A2 cache registers  216  of the transmitter  202 . The implementation of the cache registers  216  is disclosed in related U.S. patent application No. ______ entitled Cache for EEPROM Emulation using Firmware Controller in a Fiber-Optic Transceiver filed on ______ which is assigned to Agilent Technologies of Palo Alto, Calif. and is incorporated by reference. Although the bus  215  is described as “external” a portion of the bus  215  may be disposed within the module  200 . Consequently, “external” refers to the fact that the bus  215  allows a direct connection between one or more external devices  220  and the A1 and A2 cache registers  216   
         [0015]    During normal operation, the external device  220  accesses a particular register within cache registers  216  with a three cycle access procedure. During the first cycle, the external device  220  sends an address on the external bus  215  that selects either the A1 or A2 registers  216 . Then, the external device  220  sends an offset value on the external bus  215  that indicates which of the registers within the selected A 1  or A 2   216  registers that is to be accessed. Third, data is written from the external device  220  to the selected cache register  216 , or the external device  220  reads data from the selected cache register  216 . Since, during normal operation, the external device  220  only has access to the A1 and A2 cache registers  216 , it does not have direct access to other internal registers that are coupled to the internal bus  205 . That is, the external device  220  does not have direct access to the internal bus  205  during normal operation of the module  200 . Not allowing the external device  220  direct access to the internal bus  205  during normal operation is typically desired because the external device  220  may interfere with the operation of the internal bus  205  or vice versa. Furthermore, by not allowing the external device  220  direct access to the internal bus  205  during normal operation, the traffic on the internal bus  105  is hidden.  
         [0016]    As was discussed above, during testing or troubleshooting of the communication module  200 , it is often desirable to monitor the data traffic on the internal bus  205  and to read from and write to registers such as the A3 registers  210  and A4 registers  211 , that are directly accessible only via the internal bus  205 . Thus, the transmitter  202  includes an analog switch circuit  230  that connects the internal bus  205  to the external bus  215  when closed. For example, the switch circuit  230  could be closed during diagnostics, verification, and fault analysis to allow an external device  220  coupled directly to the external bus  215  to monitor the data traffic on the internal bus  205  or to control the components of the module  200  connected to the internal bus  205 . To allow the direct connection between the busses  205  and  215  as provided by the switch circuit  230 , the internal bus  205  and external bus  215  are compatible or identical, both in physical structure and in protocol. If the busses  205  and  215  have multiple lines, then the switch circuit  230  may include individual switches (such as transistors, not shown) to connect the lines of the internal bus  205  to the lines of the external bus  215 , respectively. If, however, the internal bus  205  and external bus  215  have different physical structures or different protocols, then the module  200  may include a more complex bus interface (not shown) between the internal bus  205  and the external bus  215 .  
         [0017]    Still referring to FIG. 2, one or more A5 registers  240  control the operation of the switch circuit  230 . Because the A5 registers  240  are connected to the external bus  215 , and are, thus, directly accessible to the external device  220 , the external device  220  can open and close the switch circuit  230  by writing a proper data value to the A5 registers  240 . In one embodiment, the A5 register  240  is password protected with a password protection scheme (virtually any scheme can be used), so that it can only be accessed with a proper password. Therefore, during diagnostics, verification, or fault analysis, the external device  220  writes the password to a first of the A5 registers  240  and sets a flag (not shown) in a second of the A5 registers  240  to close switch circuit  230  thereby connecting the external bus  215  to the internal bus  205 . Likewise, to return to normal operation, the external device  220  clears the flag in the same manner. In one embodiment, only the manufacturer knows the password and, thus, only the manufacturer can enter the password so as to couple the internal bus  205  to the external bus  215  for diagnostics, verification, and fault analysis. Alternatively, a customer may be provided the password so that the customer can connect the internal bus  205  to the external bus  215 .  
         [0018]    Still referring to FIG. 2 as discussed above, once the external bus  215  is connected to the internal bus  205 , then the external device  220  can monitor the bus traffic on the internal bus  205  as generated by the controller  203 . Furthermore, in one embodiment, the bus protocol of both the internal bus  205  and external bus  215  allows multiple bus masters. As such, the external device  220  can actually issue commands on the internal bus  205  to control the controller  203  or to control the entire module  200 . For example, one can simulate the module  200  using a personal computer (PC) as the external device  220 . Once the desired operation is verified, the PC can load the appropriate corresponding program into the controller  203  (or into a separate memory location not shown) so that the controller  203  will operate the module  200  in the desired manner.  
         [0019]    [0019]FIG. 3 is a block diagram of a digital communication system  300  that incorporates one or more fiber-optic communication modules  200  of FIG. 2 in accordance with an embodiment of the invention. The system  300  includes devices operable to communicate digitally with each other. Such devices include high-volume database computers  305 , server computers  307 , and network devices  309  (hubs, routers, switches). A conventional TX/RX link  303  couples the devices to a communication hub  301  that is operable to house several communication modules  200 .  
         [0020]    In one embodiment, each module  200  comprises one or more channels for receiving and transmitting data via a fiber-optic network. In one embodiment, each communication module  200  incorporates eight independent data channels (four transmit and four receive channels) operating from 1 to 3.2 Gb/s per channel for digital communication between devices. Such a communication module  200  is disclosed in a related U.S. patent application No. ______ entitled Integrated Multichanned Laser Driver and Photodetector Receiver filed on Dec. 20, 2002 which is assigned to Agilent Technologies of Palo Alto, Calif. and which is incorporated by reference. The communication module  200  can then communicate with other modules through a fiber-optic communication link  302 . As such, devices such as high-volume database computers  305 , server computers  307 , and network devices  309  (hubs, routers, switches etc.) can communicate efficiently and effectively using the multichannel capabilities of the communication modules  200 .