| 摘要 |
PURPOSE:To improve the overall putthrough and to relieve the load of the CPU by so forming the system that each node transmits a frame to itself in order to test its state of coupling with the ring and by checking its result by a dedicated LSI, and further generating an interruption in the firmware based on the above result. CONSTITUTION:The transmission frame 500 from the node A goes around a ring, and is inputted to the receiving circuit of a TPC (token passing controller) 10. If the inputted byte is a source address part SA, the TPC10 compares it with its own address (MA). And the comparison-result is expressed in the third bit and the second bit of a receiving status register RXFS1028. If it is 00, then SA=MA. At this time, the outputs of an inverting circuits 1034 and 1035 shown in figure (b) become a logic 1. In case when the ring turn-around test is made valid, an FF1036 is set by an MUP20. An FF1037 is a storage element to show whether or not the status is valid, and shows that the status information is exactly set in an RXFS. Accordingly, if the circuit shown in figure (b) is used, when the bits 1036 and 1037 both are logic 1 and hence are in a valid status and if SA=MA, a turn-around interruption FF1039 is set.
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