PCR-TD20

Hi experts,

                   I'm deeply confused with TD20 PCR.As per my knowledge the TD20 pcr generates technical errors (type 3) in pair formation.What type of technical errors are generated,some times TD20 does generate clock-in and clock-out messages where as TE30 also generates the same thing, then what is the difference between TD20 and TE30???this is the very urgent requirement for me please explain the below queries with patience.

1.Which cases The TD20 generates Clock-in and clock out errors in ?

2.Difference between TD20 and TE30 ???

Regards,

Babu.M