NTRB21 DTI/PRI/DCH TMDI card Page 833 of 906Circuit Card Description and InstallationMicroprocessorThe NTRB21 is equipped with bit-slice microprocessors that handle thefollowing major tasks:• Task handler: also referred to as an executive. The task handler providesorderly per-channel task execution to maintain real-time task orderingconstraints.• Transmit voice: inserts digital pads, manipulates transmit AB bits forDS1, and provides graceful entry into T-Link data mode when the datamodule connected to the DTI/PRI trunk is answering the call.• Receive voice: inserts digital pads and provides graceful entry intoT-Link data mode when the data module connected to the DTI/PRI trunkis originating the call.• T-Link data: a set of transmit and receive vectored subroutines whichprovides T-Link protocol conversion to and from the DM-DM protocol.• Receive ABCD filtering: filters and debounces the receive ABCD bitsand provides change of state information to the system.• Diagnostics• Self-testDigital padThe digital pad is an EPROM whose address-input to data-output transferfunction meets the characteristics of a digital attenuator. The digital padaccommodates both μ255-Law and A-Law coding. There are 32combinations each for μ255 to μ255, μ255 to A-Law, A-Law to μ255, andA-Law to A-Law. These values are selected to meet the EIA loss and levelplan.
