6224d ac maindec-08-dhdpa-d-d DP8E Synchronous Modem Interface 6227d ak maindec-08-dhdpa-d-pb DP8E Synchronous Modem Interface 6224b ac maindec-08-dhdpa-b-d DP8E Synchronous Modem Interface 6227b ak maindec-08-dhdpa-b-pb DP8E Synchronous Modem Interface