Hi,
For many industral control monitor optical receivers, it defined its datarate is DC-500KHz. I wonder what ever DC mean here?It is really a very low frequency signal like low to 10Hz 010101... signal? Or it is in fact works in 500KHz, but because the long "1""0", it corresponding the verly low frequency?

There is the descranpancy between them, because the former has very slow rise/fall time @10Hz while the later still has the the sharp rise/fall time because it in fact works with the 500KHz signal but with long continuous"1" or "0".

Thanks for the help.