APPLICATION NOTE 331

DS2172, DS21372, and DS2155's BERT V.54 Modem Test Patterns


Abstract: This application note describes how to generate V.54 modem test patterns with the DS2172, DS21372, and DS2155's bit error rate tester (BERT).

Overview

The DS2172, DS21372, and the DS2155's BERT can be used to generate and detect the PREPARATORY, ACKNOWLEDGE, and TERMINATION patterns for V.54 modem testing. Figure 1 shows the pattern generator depicted in V.54. The pattern generator in the DS2172 and DS21372 is shown in Figure 2. With the SCRAMBLE input set to 1 in Figure 1 and the EIR.5 input in Figure 2 set to 1, DS2172 and DS21372 generate the same pattern if initialized to all 1's, as the V.54 circuit initialized to all 0's. V.54 requires no specific initialization value.

V.54 specifies that each pattern must be N ± 100 clocks. This must be handled external to the DS2172, DS21372 and the BERT of DS2155.

After the PREPARATORY phase, the initiating DTE must transmit an ADDRESS octet at least 16 times. The DS2172, DS21372, and DS2155's BERT can also transmit this pattern. The settings for transmitting this repetitive pattern for DS2172 and DS21372 are shown on Table 1. The repetition count must be handled externally to the DS2172, DS21372, and DS2155's BERT.

Refer to the initialization values in Table 1 and Table 2 for DS2172, DS21372, and DS2155's BERT programming.


Figure 1. V.54 CIRCUIT


Figure 2. DS2172, DS21372 PATTERN GENERATION BLOCK DIAGRAM

Notes:

  1. Tap A always equals length (N-1) of any pseudorandom or repetitive pattern.
  2. Tap B can be programmed to any feedback tap for pseudorandom pattern generation
Table 1. DS2172 and DS21372 Initialization Values
Pattern PLR PTR PSR0/1/2/3 PCR.5 EIR.5 EIR.4 Clock Burst*
PREPARATORY 06H 03H FFH 1 0 0 2055 ± 100
ACKNOWLEDGE 06H 03H FFH 1 1 1 1955 ± 100
TERMINATE 06H 03H FFH 1 1 1 8199 ± 100
ADDRESS 07H 00H ADDRESS 0 0 0 128 MIN

*7 clocks added to V.54 spec to account for delay through DS2172 and DS21372.

Table 2. DS2155's BERT Initialization Values

Pattern BC1 BC2 BRP1/2/3/4 Clock Burst**
PREPARATORY 00H 00H FFH 2055 ± 100
ACKNOWLEDGE 60H 00H FFH 1955 ± 100
TERMINATE 60H 00H FFH 8199 ± 100
ADDRESS 10H 00H ADDRESS 128 MIN

**For DS2155's BERT, the number for CLOCK BURST should be decreased by 7 clocks.