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When power is applied to the CC121 module, or the VMEbus SYSRESET* signal is activated, the onboard devices will be reset. These devices include the COM9026, the COM9032, and the board control register. After reset the ARCNET protocol controller will perform an internal initialization cycle, and reads its node ID from the Node ID switch. The COM9026 will also generate a reset interrupt. Note that this interrupt will not immediately generate a VMEbus interrupt, because the interrupt enable bit of the board control register is cleared during reset.
After successful initialization, the COM9026 will execute two write cycles to the dual-port RAM. Location 00 will be written with D1 (hex), and location 1 will be written with the Node ID value, as it was read from the Node ID switch. Only when the VMEbus master reads these patterns from the dual-port RAM, proper operation of the COM9026 is assured.
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