Nortel Circuit Card Installation Manual page 833

Microprocessor
The NTRB21 is equipped with bit-slice microprocessors that handle the
following major tasks:
• Task handler: also referred to as an executive. The task handler provides
orderly per-channel task execution to maintain real-time task ordering
constraints.
• Transmit voice: inserts digital pads, manipulates transmit AB bits for
DS1, and provides graceful entry into T-Link data mode when the data
module connected to the DTI/PRI trunk is answering the call.
• Receive voice: inserts digital pads and provides graceful entry into
T-Link data mode when the data module connected to the DTI/PRI trunk
is originating the call.
• T-Link data: a set of transmit and receive vectored subroutines which
provides T-Link protocol conversion to and from the DM-DM protocol.
• Receive ABCD filtering: filters and debounces the receive ABCD bits
and provides change of state information to the system.
• Diagnostics
• Self-test
Digital pad
The digital pad is an EPROM whose address-input to data-output transfer
function meets the characteristics of a digital attenuator. The digital pad
accommodates both µ255-Law and A-Law coding. There are 32
combinations each for µ255 to µ255, µ255 to A-Law, A-Law to µ255, and
A-Law to A-Law. These values are selected to meet the EIA loss and level
plan.
NTRB21 DTI/PRI/DCH TMDI card
Circuit Card
Page 833 of 906
Description and Installation