We designed and commissioned three data bridge interfaces that allowed individual control functions to be switched between the legacy control system and the new/future control system. The second phase of the project (65M) was contingent on the successful commissioning of the data bridge interfaces which was accomplished on budget and on schedule.
As can be seen bridge modules were added to the existing system for each of the 090/190 byte serial channels and one for the data bus controller. They are software configurable so that specific messages and specific data addresses can be passed through as before or supplanted with data from the new control system. This required custom designed hardware and embedded software.
The 090/190 communication channels carry byte-serial messages where the message length and format are signified by a id field in the message header. Bytes are 12 bits wide and a clock pulse goes from low to high when there is new data.
The modules were installed by cutting the data lines, connecting the lines coming from the 090 transmitter to the bridge module's input and connecting the data lines going to the 190 receiver to the output. The hardware design provided a pass through mode so that the legacy control system could operate as before without the benefit of the 090/190 bridge software.
In it's normal operating mode, the bridge software intercepts messages coming from the 090 transmitter and forwards them to the new level-2 control via the control signal freeway (CSF). If the message id is not mapped to the new system then it is also forwarded to the legacy 190 receiver. In addition, messages sent by the new system are are forwarded to the 190 receiver provided their id's are mapped to the new system.
The legacy I/O system is connected to the legacy level-1 mini-computer through a data bus controller. The bridge module was installed by connecting it to the existing data, address, and control bus via tri-state buffers. The DATA and MAP dual port memory was designed to occupy the same address space as the legacy I/O system. One of the data lines of the MAP memory was used as a flag bit to control the tri-state buffers so as to route output data from either the legacy bus controller or from the DATA dual port memory on an address by address basis. All input data is written to the dual port memory regardless of the flag bit.
The bridge module can operate in a passive mode, using the address and bus control signals generated by the legacy controller or it can operate in an active mode by generating the address and bus control signals itself.