RCVDL56DPFL/SP, RCV56DPFL/SP, and RCV336DPFL/SP Designer’s Guide
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14-5
For more flexibility, the user may prefer to take control over the data rate selection by monitoring EQM during phase 4 and
manually selecting the data rate based on predetermined EQM thresholds. Such a method is used in V.34 mode with the
RCV288DPx and RC336ACF/DPFL V.34 data pumps. The procedure for manual speed selection for both handshakes and
retrains is as follows:
K56flex Mode (Client Receiver):
1. Turn off the EARC bit.
2. Wait for SECTXB = 63h.
3. Wait
for
LSB of 04Dh = 02h; waiting for transmitted TRN counter to get near end.
4. Quickly read approximately 64 samples (to get a good average) of EQM at 20Ch (16-bit reads) and obtain average.
5. Based on average EQM value read, select a receive data rate by writing the value 0Xh in 2E4h where X = the
corresponding data rate as shown in Table 14-1.
V.34 Mode (Normal V.34 or Server K56flex Receive Mode):
1. Make sure EARC = 1 and ARA-in-RAM feature is enabled (3A5h:4 = 1).
2. Wait for SECRXB or SECTXB = 4Xh.
3. Read and save the symbol rate from 2E3h (will always be 3200 in K56flex mode). Based on the read symbol rate, write
the suggested ARA-in-RAM values (see Table 14-3) to the specified locations (all are 8-bit writes)
4. Wait for SECTXB = 63h (handshake and RTRN).
5. Read and save value from 39Ah; this is the data rate the ARA has selected.
6. If the value is 04h or less (9.6k or less), or the rate mask has been set to speeds of 9.6k or less, or the symbol rate is
less than 3000, end the procedure; otherwise continue.
7. Write 7800h to A29h (16-bit access), write 7F00h to B29h (16-bit access), and turn off the EARC bit; this scales the
EQM value up and turns off ARA. (These locations will automatically be restored at connect time).
8. Wait for the LSB of 04Dh = 02h; waiting for transmitted TRN counter to get near end.
9. Quickly read approximately 64 samples (to get a good average) of EQM at 20Ch (16 bit reads) and obtain average.
10. Select SPEED from Table 14-4.
Note: In step 10, 33.6k (value of 0Eh) should only be selected if the symbol rate is 3429. If the average EQM is very good,
yet the symbol rate is only 3200, then a maximum of 31.2k should be selected (value of 0Dh). If the symbol rate is 3000,
then a maximum of 26.4k should be selected (value of 0Bh). If the user has limited the data rate through the rate mask to a
value less than the one selected in step 10, the lower rate mask value will prevail.
Step 10 selects the desired RX rate and modifies it just prior to the transmission of the MP sequence. The EQM windows
listed may be altered as desired.
14.2 RETRAINS AND RENEGOTIATIONS
Retrains and rate renegotiations are handled in the same manner as in V.34 using the RTRN and RREN bits, respectively.
For retrains, the EARC bit should be left on to allow the modem to select the highest rate possible under the current
conditions. For rate renegotiations, the EARC bit should be turned off and the desired receive rate should be written to
CONF (9Xh on client modem, CXh on server modem) followed by the setting of RREN. The rate masks may also be used.
The CTS bit will turn off during the retrain or rate renegotiation process and will turn back on when completed.
The V.34 mask address at 383h/382h, which is used in V.34 mode, can still be used on the client modem when connected in
K56flex but will only affect the transmit rate (the server modem's receive rate). When connecting in K56flex mode, it's
preferable to use the new rate masks at 604h and 605h. These masks may also be used in V.34 and allow the user to
manipulate the transmit and receive speeds independently as opposed to the 383h/382h mask which limits both the transmit
and receive rate when used. Note, however, the new masks only limit the maximum data rate and do not allow the user to
selectively disable data rates (see Table 14-1).
Содержание RC336DPFL
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