15/23

MTC20455

Figure 7. ATM Specific TC Layer Functions

DMT Symbol Timing Unit (DSTU)

The DSTU interfaces with various modules, like DSP Front-End, FFT/IFFT, Mapper/Demapper, RS, Mon-

itor and Transceiver Controller. It consists of a real time and a scheduler module. The real time unit gen-

erates a time-base for the DMT symbols (sample counter), superframes (symbol counter) and

hyperframes (sync counter). The timebases can be modified by various control features. They are contin-

uously fine-tuned by the DPLL module. The DSTU schedulers execute a program, controlled by program

opcodes and a set of variables, the most important of which are real time counters. The transmit and re-

ceive sequencers are completely independent and run different programs. An independent set of variables

is assigned to each of them. The sequencer programs can be updated in real time.

Interface Module

The interface module collects cells (from the cell-based function module) or a byte stream (from the de-

framer). Cells are stored in FIFO’s (424 bytes or 8 cells wide, transmit buffers have the same size), from

which they are extracted by the interface submodule, providing an Utopia level 2 interface.

Analog Front-End Control Interface

The Analog Front-End Interface is designed to be connected to the MTC20154 or MTC20454 Analog

Front-End component Transmit Interface The 16 bit words are multiplexed on 4 AFTXD output signals. As

a result 4 cycles are needed to transfer 1 word. Refer to Table 10 for the bit/pin allocation for the 4 cycles.

The first of 4 cycles is identified by the CLWD signal (Fig.7). The Analog Front-End fetches the 16 bit word

to be multiplexed on AFTXD from the Tx Digital Front-End module.

Table 10. Bits assigned to pins/time slot for single line interface

Cycle 0

Cycle 1

Cycle 2

Cycle 3

AFRXD_i[0]

b0

b4

b8

b12

AFRXD_i[1]

b1

b5

b9

b13

AFRXD_i[2]

b2

b6

b10

b14

AFRXD_i[3]

b3

b7

b11

b15

GP_IN

t0

t1

t2

t3

From Generic TC

FAST

SLOW

To Interface

Module

Cell

Descrambler

Synchronizer

HEC

Cell filter

Cell

Descrambler

Synchronizer

HEC

Cell filter

BER

BER