The digital input card scans all the channels with a resolution of 0.5 ms with an internal buffer of 4 values with time stamp per channel. The four values stored in the buffer are 3 oldest and one latest. The card holds these values until retrieved by CPU at a slower pace.
This feature of time stamping at the card level provides true 1 ms resolution as each card provides its own time stamp independent of the other. In case the time stamping is provided by the CPU, the 1 ms resolution is lost if related events are acquired from two different cards. All the cards are time synchronized by the CPU at the end of minute.
Once the data is acquired by CPU, it is transferred to the protocol specific buffer for reporting to master station. The protocol buffer can hold upto 1000 events which are retained after power failure. The overflow of internal buffer storage in communicated to master station through protocol specific diagnostic messages.