A N 9 3
176
Rev. 1.4
The ISOmodem has an internal analog-to-digital converter used to monitor the loop voltage when on-hook and
loop current when off-hook to check for parallel devices going off-hook. The host measures loop voltage and
current by reading U79 [4:0] (LVCS) or U6C[15:8] (LVS) and U63[15:8] (LCS). To set the ISOmodem to monitor
loop voltage in the on-hook state, the host issues the following commands:
To set the ISOmodem to monitor loop current, the host issues the following commands:
6.7. Modem-On-Hold
The Si2494/93 supports modem-on-hold as defined by the ITU-T V.92 specification. This feature allows a
connected Si2494/93 to place a server modem on hold while a second call, typically a voice call, uses the phone
line. The maximum time the modems will remain on hold is controlled by the modem receiving the modem-on-hold
request. Once the second call has ended, the Si2494/93 will reinitiate the data connection if the time elapsed has
not exceeded the time negotiated by the two modems. The Si2494/93 can also be placed on hold itself by a remote
modem allowing a far-end user to make or receive a voice call. Modem-on-hold is only supported on the Si2494/93
for V.34 (14400–33600 bps) and higher speed modulations. The AT+PMH command is used to enable (+PMH = 0)
or disable (+PMH = 1) modem-on-hold.
6.7.1. Initiating Modem-On-Hold
Modem-on-hold is typically initiated when a connected client modem receives a subscriber alert signal (SAS) tone
as described in "6.5. Type II Caller ID/SAS Detection" on page 163. However, it may be initiated any time the
modem is on-line in command mode. The AT+PMHR command is used to initiate a modem-on-hold request. After
this command is issued, the modem will place a modem-on-hold request to the server, and the +PMHR: command
response will indicate the server’s response to the request. The possible responses are shown in Table 117.
If the server refuses to grant a modem-on-hold request, the modem will use the +PMHT setting to determine what
to do. If +PMHT = 0, the modem will remain connected to the server. If +PMHT is set to a non-zero value, the
modems will disconnect. The Si2494/93 will indicate these conditions with the result code, “MHnack;
Disconnecting…” or “MHnack; Reconnecting…”
Once modem-on-hold has been initiated, it may be necessary for the Si2494/93 to perform a hook-flash to indicate
to the central office the incoming call may be accepted. This is initiated with the AT+PMHF command. The Si2494/
93 will go on-hook for the time set in user register U4F and remain off-hook while on-hold. Usually, a second hook-
flash is necessary to reestablish a data connection with the remote modem.
The Si2494/93 will attempt to reestablish a data connection with the remote modem upon receipt of the ATO
command and will indicate the connection has been reestablished with the CONNECT message. If the modems fail
to renegotiate the connection, the Si2494/93 will send the NO CARRIER message.
Command
Function
AT:R6C
Host reads the loop voltage
from the LVS Register U6C
bits 15:8 while the modem is
on-hook.
Command
Function
ATH1
To go off-hook
AT:R63
Host reads loop current from
the LCS Register U63 bits
15:8 while the modem is off-
hook.
Содержание Si2404
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Страница 200: ...AN93 200 Rev 1 4 Figure 31 TAM Handset and Speakerphone Voice Paths ...
Страница 201: ...AN93 Rev 1 4 201 Figure 32 Si3000 Codec Gain and Signal Selection Options ...
Страница 290: ...AN93 290 Rev 1 4 Figure 57 256 Band Spectral Display Figure 58 2048 Band Spectral Display ...
Страница 305: ...AN93 Rev 1 4 305 Figure 76 Parallel or SPI Port Interrupt Service Flowchart ...