Silicon Laboratories SI2493/57/34/15/04 - Manual (Page 253)

AN93
Rev. 1.3 253
The data sent during &T4 and &T5 transmission tests is controlled by the S40 register. The data rate for &T4 and
&T5 commands is controlled by the existing &G command. In V.34 cases, where a data rate may use multiple
symbol rates, the symbol rate is controlled by the S41 register. If an invalid combination of data/symbol rate is
selected, the modem chooses a valid symbol rate. It is the responsibility of the operator to select valid
combinations for testing.
After the &T4 or &T5 command is issued and the modulation output has begun, a result code stating CONNECT
followed by the data rate (as if the output were an actual connection) is sent. The 300 bps rate does not give the
speed after CONNECT. The &G4 command allows V.34/2400bps operation, and &G3 allows V.22bis/1200 bps
operation.
The answer tone output must also be measured during homologation testing. A bit in memory allows a continuous
answer tone to be output in the same way as a continuous DTMF tone through the AT*Y1 command. After issuing
the commands AT&H10 and AT*Y2A, a constant answer tone is produced, and the modem is returned to command
mode. Both AT commands need to be sent for each and every tone to be produced. Each of the two commands
need to be on its own command line. The tone continues until a character is received or the S7 timer expires. After
the command has been terminated, the modem returns on-hook and sends the NO CARRIER message.
For homologation testing, it may be necessary to output the V.29 modulation with transmit data. The +FTM
command includes additional codes given in Table 154 to initiate output with the transmit data specified in S40.
The AT+FCLASS=0 command must be sent before any other analoop test or connection is made. The modem
must remain on-hook for a time programmed in S-register 50. Any attempt to go off-hook is delayed by this time in
1 s units. S-50 default is 3 seconds.
There is a double CONNECT message for analoop in B1O3, V.21, and V.23 for all options except \V0.
10.4.1. EMI
The ISOmodem chipset and recommended DAA schematic are fully compliant with and pass all international
electromagnetic emissions and conducted immunity tests (including FCC parts 15 and 68; EN50082–1). Careful
attention to the ISOmodem schematic (page 47), bill of materials (page 48), and layout guidelines ensure
compliance with these international standards. In designs with difficult layout constraints, the addition of R12 and
R13 to the C8 and C9 recommended capacitors may improve modem performance on emissions and conducted
immunity. For such designs, a population option for R12 and R13 may allow additional flexibility for optimization
after the printed circuit board has been completed. Also, under some layout conditions, C8 and C9 may improve
the immunity to telephone-line transients.
Table 153. Symbol/Data Rate
S41 V.34 Symbol Rate Allowable Data Rates
0 (default) 2400 symbols/second 2400–21600
1 2743 symbols/second 4800–26400
2 2800 symbols/second 4800–26400
3 3000 symbols/second 4800–28800
4 3200 symbols/second 4800–31200
5 3429 symbols/second 7200–33600
Table 154. V.29 Data Rate
+FTM= Transmit Modulation Data Rate
53 V.29 7200
55 V.29 9600