si2439-a-gm Silicon Laboratories, si2439-a-gm Datasheet - Page 24

• Manufacturer Part Number: si2439-a-gm
• Description: V.92 And V.34 Isomodem With Global Daa
• Manufacturer: Silicon Laboratories

Si2494/39
4.17. Overcurrent Detection
The Si2494/39 includes an overcurrent detection feature that measures the loop current at a programmable time
after the Si2494/39 goes off-hook. This allows the Si2494/39 to detect if it is connected to an improper telephone
line. The overcurrent detection feature may be enabled by setting the OCDM bit (U70, bit 11). OHT (U77, bits 8:0)
sets the delay after off-hook until the loop current is measured. See “AN93: ISOmodem
Guide” for details.
4.18. Global Operation
The Si2494/39 chipset contains an integrated silicon direct access arrangement (Silicon DAA) that provides a
programmable line interface to meet international telephone line interface requirements. “AN93: Modem Designer’s
Guide” gives the DAA register settings required to meet international PTT standards.
Additionally, the user-access registers (via the AT:U and AT:R commands) may be programmed for country-specific
settings, such as dial tone, ring, ringback, and busy tone. See AN93 for complete details.
4.19. Firmware Upgrades
The Si2494/39 contains an on-chip program ROM that includes the firmware required for the features listed in this
data sheet. In addition, the Si2494/39 contains on-chip program RAM to accommodate minor changes to the ROM
firmware. This allows Silicon Labs to provide future firmware updates to optimize the characteristics of new modem
designs and those already deployed in the field. See AN93 for complete details.
4.20. DTMF Detection / Generation
The Si2494/39 provides comprehensive DTMF tone generation and detection. The ISOmodem can generate
single tones or DTMF tones using the +VTS command. DTMF tones may also be generated during dialing using
the “ATDT” command. DTMF detection is only available in voice mode (FCLASS = 8). DTMF digits are reported
from the modem to the host using <DLE> shielding.
24
LVCS
BITS
30
25
20
15
10
5
0
0 3 6 9 12 15 18 21 24
CTR21 only
27
30 33 36 39 42 45 48 51 54 57 60 63 66 69 72
Figure 9. Loop Current
Rev. 1.0
Loop Current
(mA)
75 78 81 84 87 90 93
Overload
®
Chipset Family Designer's
140