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.
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.
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.
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.