The Si2400 ISOmodem™ i s a complete modem chipset with integr ated
direct access arrangement (DAA) that provides a programmable line
interface to meet global te lephon e line r equir emen ts. Available in two 16pin small outline (SOIC) packag es, it eliminates the need for a se parate
DSP data pump, modem controller, analog front end (AFE), isolation
transformer, relays, opto-isolators, 2- to 4-wire hybrid, and voice codec.
The Si2400 is ideal for embedd ed modem applications due to its small
board space, low power consumption, and global compliance.
Ambient TemperatureT
Ambient TemperatureT
Si2400 Supply Voltage, Digital
Notes:
1. The Si2400 specifications are guaranteed when the typical application circuit (including component tolerance) and any
Si2400 and any Si3015 are used. See Figure3 on page 9 for typical application circuit.
2. All minimum and maximum specifications are guaranteed and apply across the recommended operating conditions.
Typical values apply at nominal supply voltages and an operating temperature of 25 °C unless otherwise stated.
3. The digital supply, V
from 3.3 V. The 3.3V operation applies to both the serial port and the digital signals CTS
.
RESET
3
, can operate from eit her 3.3 V or 5.0 V. The Si 2400 inte rface suppo rts 3.3V logic when operating
D
SymbolTest Condition
A
A
V
D
K-Grade02570°C
B-Grade–402585°C
Min
2
Typ
Max
2
3.03.3/5.05.25V
, CLKOUT, GPIO1–4, and
Unit
Table 2. DAA Loop Characteristics
(VD = 3.0 to 3.6 V or 4.75 to 5.25 V, TA = 0 to 70°C
for K-Grade, TA = –40
to 85°C for B-Grade)
ParameterSymbolTest ConditionMinTypMaxUnit
DC Termination VoltageV
DC Termination VoltageV
DC Termination VoltageV
DC Termination VoltageV
DC Termination VoltageV
DC Termination VoltageV
DC Termination VoltageV
DC Termination VoltageV
On Hook Leakage CurrentI
Operating Loop CurrentI
Operating Loop CurrentI
TR
TR
TR
TR
TR
TR
TR
TR
LK
LP
LP
DC Ring Current——20µA
Ring Detect VoltageV
Ring Detect VoltageV
Ring FrequencyF
RD
RD
R
Ringer Equivalence Number*REN——0.2
*Note:C15, R14, Z2, and Z3 not installed.
IL = 20 mA, ACT = 1
——7.5V
DCT = 11 (CTR21)
IL = 42 mA, ACT = 1
——14.5V
DCT = 11 (CTR21)
IL = 50 mA, ACT = 1
——40 V
DCT = 11 (CTR21)
IL = 60 mA, ACT = 1
40——V
DCT = 11 (CTR21)
IL = 20 mA, ACT = 0
——6.0V
DCT = 01 (Japan)
IL = 100 mA, ACT = 0
11——V
DCT = 01 (Japan)
IL = 20 mA, ACT = 0
——7.5V
DCT = 10 (FCC)
IL = 100 mA, ACT = 0
12——V
DCT = 10 (FCC)
V
= –48 V——1µA
BAT
FCC/Japan Modes13—120mA
CTR2113—60mA
RT = 011—22V
RT = 117—33V
15—68Hz
RMS
RMS
4 Rev. 0.95
Si2400
Table 3. DC Characteristics
(VD = 4.75 to 5.25 V, TA = 0 to 70°C
ParameterSymbol Test ConditionMinTypMaxUnit
for K-Grade, TA = –40
to 85°C for B-Grade)
High Level Input VoltageV
Low Level Input VoltageV
High Level Output VoltageV
Low Level Output VoltageV
Low Level Output Voltage, GPIO1–4V
Input Leakage CurrentI
Power Supply Current, Digital*I
Power Supply Current, DSP Power Down*I
Power Supply Current, Wake-On-Ring (ATZ)I
Power Supply Current, Total Power DownI
*Note: Specifications assume MCKR = 0 (default). Typical value is 4 mA lower when MCKR = 1 and 6 mA lower when
MCKR = 2,3.
Measurements are taken with inputs at rails and no loads on outputs.
High Level Input VoltageV
Low Level Input VoltageV
High Level Output VoltageV
Low Level Output VoltageV
Low Level Output Voltage, GPIO1–4V
Input Leakage CurrentI
Power Supply Current, DigitalI
Power Supply Current, DSP Power DownI
Power Supply Current, Wake-On-RingI
Power Supply Current, Total Power DownI
*Note: Specifications assume MCKR = 0 (default). Typical value is 2 mA lower when MCKR = 1 and 3 mA lower when
MCKR = 2,3.
Measurements are taken with inputs at rails and no loads on outputs.
(VD = 3.0 to 3.6 V or 4.75 to 5.25 V, TA = 0 to 70°C
ParameterSymbolTest ConditionMinTypMaxUnit
Transmit Frequency ResponseLow –3 dB Corner—5—Hz
Receive Frequency ResponseLow –3 dB Corner—5—Hz
Transmit Full Scale Level
Receive Full Scale Level
Dynamic Range
Dynamic Range
Dynamic Range
3,4
3,5
3
Transmit Total Harmonic Distortion
Transmit Total Harmonic Distortion
Receive Total Harmonic Distortion
Receive Total Harmonic Distortion
Dynamic Range (Caller ID mode)DR
Caller ID Full Scale Level (0 dB gain)
Notes:
1.
Measured at TIP and RING with 600 Ω termination.
2. Receive full scale level will produce –0.9 dBFS at TXD.
3. DR = VIN + 20*log (RMS signal/RMS noise). Measurement is 300 to 3400 Hz. Applies to both transmit and receive
(VD = 3.0 to 3.6 V or 4.75 to 5.25 V, TA = 0 to 70°C
ParameterSymbolTest ConditionMinTypMaxUnit
AOUT Dynamic Range, APO = 0VIN = 1 kHz—40—dB
AOUT THD, APO = 0VIN = 1 kHz—–40—dB
AOUT Full Scale Level, APO = 0—0.7*V
AOUT Mute Level, APO = 0—60—dB
AOUT Dynamic Range, APO = 1,
V
= 4.75 to 5.25 V
D
AOUT Dynamic Range, APO = 1,
V
= 3 to 3.6 V
D
AOUT THD, APO = 1, V
5.25 V
AOUT THD, APO = 1, V
AOUT Full Scale Level, APO = 1—1.5—V
AOUT Mute Lev el, APO = 1—–65—dB
AOUT Resistive Loading, APO = 110——kΩ
AOUT Capacitive Loading, APO = 1——20pF
AIN Dynamic Range, V
5.25 V
AIN Dynamic Range, V
AIN THD, V
AIN THD, V
= 4.75 to 5.25 VVIN = 1 kHz, –3 dB–55–60—dB
D
= 3 to 3.6 VVIN = 1 kHz, –3 dB–40–60—dB
D
AIN Full Scale Level
*Note: Receive full scale level will produce –0.9 dBFS at TXD.
= 4.75 to
D
= 3 to 3.6 VVIN = 1 kHz, –3 dB–40–60—dB
D
= 4.75 to
D
= 3 to 3.6 VVIN = 1 kHz, –3 dB5565—dB
D
*
for K-Grade, TA = –40
VIN = 1 kHz, –3 dB6065—dB
VIN = 1 kHz, –3 dB5565—dB
VIN = 1 kHz, –3 dB–55–60—dB
VIN = 1 kHz, –3 dB6065—dB
to 85°C for B-Grade)
—2.8—V
DD
—V
PP
PP
PP
Table 7. Absolute Maximum Ratings
ParameterSymbolValueUnit
DC Supply VoltageV
Input Current, Si2400 Digital Input PinsI
Digital Input VoltageV
Operating Temperature RangeT
Storage Temperature RangeT
Note: Permanent device damage may occur if the above Absolute Maximum Ratings are exceeded. Functional operation
should be restricted to the conditions as specified in the operational sections of this data sheet. Exposure to absolute
maximum rating conditions for extended periods may affect device reliability.
D
IN
IND
A
STG
Rev. 0.957
–0.5 to 6.0V
±10µA
–0.3 to (VD + 0.3)V
–10 to 100°C
–40 to 150°C
Si2400
Table 8. Switching Characteristics
(VD = 3.0 to 3.6 V or 4.75 to 5.25 V, TA = 0 to 70°C
ParameterSymbolMinTypMaxUnit
CLKOUT Output Clock Frequency2.4576—39.3216MHz
Baud Rate Accuracyt
Start Bit ↓ to CTS
CTS
↓ Active to Start Bit↓t
RESET
RESET
Note:
↓ to RESET
↑ Rise Timet
All timing is referenced to the 50% level of the waveform. Input test levels are VIH = VD – 0.4 V, VIL = 0.4 V
TXD
↑t
↑t
for K-Grade, TA = –40
bd
sbc
csb
rs
rs2
–1—1%
—1/(2*Baud Rate)—ns
10——ns
5.0——msec
——100ns
Transmit Timing
to 85°C for B-Grade)
8-Bit Data
Mode (Default)
TXD
9-Bit Data
Mode
RXD
8-Bit Data
Mode(Default)
RXD
9-Bit Data
Mode
t
csb
CTS
StartD0D1D2D3D4D5D6D7Stop
StartD0D1D2D3D4D5D6D7Stop
D8
Receive Timing
StartD0D1D2D3D4D5D6D7Stop
StartD0D1D2D3D4D5D6D7Stop
t
sbc
D8
Note: Baud rates (programmed through register SE0) are as follows: 300, 1200, 2400, 9600, 19200,
230400, 245760, and 307200 Hz.
Figure 2. Asynchronous UART Serial Interface Timing Diagram
8 Rev. 0.95
Typical Application Circuit
VCC
C10
C27
C26
X1
12
GPIO3/AIN/ESC
GPI O2/ AIN/ RXD2
GPI O1/ AIN/ TXD2/ EO FR
U1
CLKOUT
RESET
1
XTALI
2
XTALO
3
CLKOUT
4
VD
TXD
RXD
CTS
5
TXD
6
RXD
7
CTS
89
RESETAOUT
GPIO4/AIN/ALERT
Si2400
AOUT
GPIO1
GPIO2
GPIO3
ISOB
GND
GPIO4
16
15
14
13
12
11
C1A
10
C30
C3
Rev. 0.959
No Ground Plane I n DAA S ection
R8
R7
R15
1
2
3
4
5
6
C1
C2
C4
7
89
U2
TSTA/Q E2
TX/FILT2
TSTB/ DCT
NC/FI LT
IGND
C1B
REXT
RNG1
DCT/REX T2
RNG2
NC/REF
QB
NC/VREG2
QEVREG
5
Si301
Q4
C12
C13
+
16
15
14
RX
13
12
11
10
R11
C6
C19
C18
R12
C16
C14
+
+
C5
R2
R13
C8
C7
R10
R9
R24
R18
Z1
Q1
R5
Q2
R6
C20
R16
R19
R17
Q3
FB2
D2
C9
RV2
D1
R26
R25
C25
C24
FB1
RING
C32
RV1
C31
TIP
Note 1:R12 R13 and C14 are onl requiredif complexAC terminationis used ACT bit 1 .
1. C2 was included in previous revisions of the data sheet. Replacing C2 with C4 improves longitudinal balance.
2. For FCC-only designs: C14, R12, and R13 are not required; R2 may be ±5%; with Z1 rated at 18 V, C5 may be rated at 16 V; also see note 7.
3. C30, C31, C32 may provid e an additio nal improvement in emissions/immunity and/or voice performance, depending on design and layout. Population
option recommended. See "Emissions/Immunity‚" on page 62.
4. Several diode bridge configurations are acceptable (suppliers include General Semi., Diodes Inc.).
5. Q4 may require copper on board to meet 1/2 W power requirement. (Contact manufacturer for details.)
6. RV2 can be installed to improve performance f rom 2500 V to 3500V for multiple longit udinal surges (240 V, MOV).
7. The R7, R8, R15, and R16, R17, R19 resistors may each be replaced with a single resistor of 1.62 kΩ, 3/4 W, ±1%. For FCC-only designs, 1.62 kΩ, 1/16
W, ±5% resistors may be used.
150 pF, 3 kV, X7R,±20%Not Installed
0.1 µF, 50 V, Elec/Tant/X7R, ±20%
0.68 µF, 16 V, X7R/Elec/Tant, ±20%
10 pF, 16 V, NPO, ±10%Not Installed
1000 pF, 3 kV, X7R, ±10%Not Installed
Dual Diode, 300 V, 225 mACentral Semic onductor
BCP56, NPN, 60 V, 1/2 WOnSemiconductor, Fairchild
240 V, MOVNot Installed
402 Ω, 1/16 W, ±1%
4.87 kΩ, 1/4 W, ±1%
78.7 Ω, 1/16 W, ±1%
215 Ω, 1/16 W, ±1%
Zener Diode, 43 V, 1/2 WVishay, Motorola, Rohm
10 Rev. 0.95
Si2400
Analog Input/Output
Figure 4 illustrates a n optional application circuit to support the analog output ca pability of the Si2400 for voi ce
monitoring purposes.
+5V
C2
AOUT
R3
C6
R1
6
3
2
5
U1
4
C3
C4
C5
Speaker
R2
Figure 4. Optional Connection to AOUT for a Monitoring Speaker
‘
Table 10. Component Va lues—Optional Connection to AOUT
The Si2400 ISOmodem is a complete modem chipset
with integrated direct access arrangement (DAA) that
provides a programmable line interface to meet global
telephone line requirements. Available in two 16-pin
small outline pa cka ge s, this sol ut io n inc lud es a D SP dat a
pump, a modem co ntroller, an analog fron t end (AFE), a
DAA, and an audio co de c.
The modem, which accepts simple modem AT
commands, provides connect rates of up to 2400 bps,
full-duplex over the Public Switched Telephone Network
(PSTN) with V.42 hardware support through HDLC
framing. To minimize handshake times, the Si2 400 can
implement a V.25-based fast connect feature. The
modem also su pp or ts the V.23 reversing pr oto col a s we ll
as SIA and other al ar m sta nd ard fo rma t s.
As well as suppor ting the modem si gnallin g proto cols, th e
ISOmodem provides numerous additional features for
embedded mode m ap pl ic a ti on s. T he S i 24 00 in c lu de s full
caller ID detection and decoding for the US, UK, and
Japanese caller ID formats. Both DTMF decoding and
generation are prov ided on chip a s well. Call pro gres s is
supported both at a high level through echoing result
codes and at a low level through user-programmable
biquad filters and parameters such as ring period, ring
on/off time, and dialing interdigit time.
This device is ideal for embedded modem applications
due to its small board space, low power consumption,
and global compliance. The Si2400 solution integrates a
silicon DAA using Silicon Laboratories’ proprietary
ISOcap™ technology. This highly integrated DAA can be
programmed to meet worldwide PTT specifications for
AC termination, DC termination, ringer impedance, and
ringer thresh old. The DAA a lso can mon itor l ine st atu s for
parallel handset detection and for overcurrent conditions.
The Si2400 is designed so that it may be rapidly
assimilated into existing modem applications. The device
interfaces directly through a UART to either a
microcontroller or a standard RS-232 connection. This
simple interfa ce allows for PC evalua tion of the modem
immediately up on po we rup v i a t he AT commands across
a standard hyperterminal.
The chipset can be fully programmed to meet
international telephone line interface requirements with
full compliance to FCC, CTR21 , JATE, and other countryspecific PTT specifications. In addition, the Si2400 has
been designed to meet the most stringent worldwide
requirements for out-of-band energy, billing-tone
immunity, lightning surges, and safe ty re qu ire me nts .
The Si2400 solut ion needs only a few low-cost disc rete
components to achieve global compliance. See Figure 3
on page 9 for a typi cal ap pli cati on cir cu it .
V.23 1300/1700600/75
Bell 103FSK1170/2125300Full
Bell 212ADPSK1200/24001200Full
SecurityDTMF—40Full
SIA—PulsePulse—LowFull
SIA FormatFSK1 170/2125300 half-duplex300 bps only
*Note: The Si2400 only adjusts its baud ra te for li ne condi tions during the in itiali zation of the ca ll. Retra ining to a ccommo date
changes in line conditions which occur during a call must be implemented by terminating the call and redialing.
Carrier
Frequency (Hz)
1300/21001200/75
Data Rate
(bps)
Standard
Compliance
Full; plus reversing
(Europe)
12Rev. 0.95
Si2400
Digital Interface
The Si2400 has an asynchronous serial port (UART)
that supports st andard microcontroller interfaces. After
reset, the baud rate defaults to 2400 bps with the 8-bit
data format described bel ow. Immediately after powerup, the device must be progr ammed using the primary
serial port because the secondary serial port is disabled
by default. The CLKOUT clock will be running with a
frequency of 9.8304 MHz.
The baud rate of the serial l ink is e stablished by writin g
S register SD (SE0.2:0). It may be set for 300, 1200,
2400, 9600, 19200, 228613, 245760, or 307200 bps.
Immediately after the ATSE0=xx string is sent, the user
must reprogram the host UART to matc h the selected
new baud rate. The higher baud rate settings (>230400)
can be used for tra nsferring PCM d ata from the host to
the Si2400 for transmission of voice data over the
phone line or through the voice codec.
Table 12. Register S07 Examples: DTMF = 0,
HDEN = 0, BD = 0
Modem ProtocolRegister S07 Values
data bits, and the line data fo rmat is 8 data bits (8N1),
then the MSB from the l ink will be dropped as the 9-bit
word is passed from the link sid e to the line si de. In this
case, the dropped ninth bit can then be used as an
escape mechanism. However, if the link data format is 8
data bits and the line data fo rm at i s 9 data b its , an MSB
equal to 0 will be added to the 8- bit wor d as it is pas se d
from the link side to the line side.
The Si2400 UART does not continuou sly c heck for sto p
bits on the incom ing digital data. Ther efore, if the RXD
pin is not high, the TXD pin may transmit mean ingless
characters to the host UART. This requires the host
UART to flush its receiver FIFO upon initialization.
The Si2400 can be configured to any of the Bell and
CCITT operation modes. This device also suppo rts SIA
and other security modes for the security industry.
Table 11 provides the modulation method, the carrier
frequencies, the data rate, the baud rate and the notes
on standard complianc e for each modem configuratio n
of the Si2400. Table 12 shows example register settings
(SO7) for some of the modem configurations.
As shown in Figure 6, 8-bit a nd 9-bit data modes refer
to the link data format over the UART. Line data formats
are configured through registers S07 and S15. If the
number of bits specified by the link data format differs
from the number of bits specified by the line data
format, the MSBs will either be dropped or bit-stuffed,
as appropriate. For ex ample, if th e link data forma t is 9
Command/Data Mode
Upon reset, the modem will be in command mode and
will accept AT-style commands. An outgoing modem
call can be made using the “ATDT#” (tone dial) or
“ATDP#” (pulse dial) command after the device is
configured. If the handshake is successful, the modem
will respond with the “c”, “ d”, o r “v ” str i ng an d en ter data
mode. (The byte following the “ c”, “d”, or “v” will be the
first data byte.) At this point, A T-style commands are not
accepted. There a re thre e meth ods whic h may be u sed
to return the Si2400 to command mode:
!
Use the ESC pin—To program the GPIO3 pin to
function as an ESCAPE input, set GPIO3
(SE2.5:4) = 3. In this setting, a positive edge
detected on this pin will return the modem to
command mode. The “AT O” string can be used to reenter data mode.
!
Use 9-bit data mode—If 9-bit data format with
escape is programmed, a 1 detected on bit 9 will
return the modem to command mode. (See Figure 2
on page 8.) This is enabled by setting ND (SE0.3) =
1 and NBE (S15.0) = 1. The “ATO” string can be
used to reenter data mode.
!
Use TIES—The time independent escape sequence
is a sequence of three escape characters ("+"
characters by default). Once these characters have
been recognized, the modem enters the Command
state without sending a confirming result code to the
terminal. The modem then starts an internal prompt
Rev. 0.9513
Si2400
delay timer. From that point on if an AT<CR>
(attention) command is received before the timer
expires, the timer is stopped and the “O” response
code is sent to the terminal. This indicates that the
Si2400 is in command mode.
If any other data is received while the timer is
running, the timer is stopped, the device returns to
the online state, and the data received through the
UART RXD is sent to the other modem.
If the timer expires, a confirming “O” response code
is sent to the terminal indicating that the modem is in
command mode.
TIES can be enabled by writing register TED
(S14.5)=1. Both the escape character “+” and the
escape time-out period are programmable via
registers TEC (S0F) and TDT (S10), respectively.
Note: TIES is not the recommended escape solution for the
most robust designs. Any data strings that actually
contain the escape character three times in a row will
interrupt a data sequence erroneously.
Whether using an escape method or not, when the
carrier is lost, the modem will automatically return to
command mode and report “N”.
8-Bit Data Mode
This mode is asynchronous, full-duplex, and uses a
total of 10 bits (shown in Figure 2 on page 8). To
program 8-Bit Data mode, set ND (SE0.3) = 0. (Note
that 8-Bit Data mode is the defa ult.) The 10 bi ts consist
of a start bit (logic 0), 8 data bits, and 1 stop bit (logic 1).
Data transmission from the Si2400 to the host takes
place on the TXD pin. It beg ins whe n th e Si 24 00 l owers
TXD, placing the start bit on the pin. Data is then shifted
out onto the pin, LSB fi rst. After 8 data bits, th e stop bit
follows. All bits are s hi fted out a t the ra te d etermi ne d by
the baud rate register.
Once the baud rate register SD (SE0.2:0) is written,
reception by the Si2400 may begin at any time. The
falling edge of a start bit will signal to the Si2400 that the
reception process has begun. Data should be shifted
onto RXD at the selected baud rate.
After the middle of the stop-bit time, the receiver will go
back to looking for a 1 to 0 transition on the RXD pin.
9-Bit Data Mode
This mode uses a total of 11 bits in UART
communication. To program 9-Bit Data mode, set ND
(SE0.3) = 1. The 11 bits consist of one start bit (logic 0),
9 data bits, and 1 stop bit (logic 1, see Figure 2 on page
8). As in 8-Bit Data mode, the trans missions occur on
the TXD signal pin and receptions on the RXD pin.
Data transmission from the Si2400 to the host takes
place on the TXD pin. It beg ins whe n th e Si 24 00 l owers
TXD, placing the start bit on the pin. Data is then shifted
out onto the pin, LSB fi rst. After 9 data bits, t he stop bit
follows. All bits are shifted out a t the rate d eterm ine d by
the baud rate register.
Once the baud rate register SD (SE0.2:0) is written,
reception may begin at any tim e. The falling edge of a
start bit on the RXD pin will begin the reception process.
Data must be shifted in at the selected baud rate.
The ninth data bit may be used to indicate an escape by
setting NBE (S15.0) = 1. If so, this bi t will normally be
set to 0 when the modem is online. To go offline into
command mode, se t th is b it to 1. The next fram e wi ll b e
interpreted as a command. Data mode can be
reentered using the ATO command.
After the middle of the stop-bi t time, the rece iver will go
back to looking for a 1 to 0 transition on the RXD pin.
Flow Control
If a higher serial link line (UART) data rate is
programmed than the baud rate of the modem, flow
control is required to prevent loss of data to the
transmitter. No flow control is nee ded if the same baud
rate as modem rate is programmed. Note that in
compliance with the V.22bis algorithm, the V.22bis
(2400 baud) modem will connect at 1200 baud if it
cannot make a 2400 baud connection.
To control flow, the CTS
Figure 2 on page 8, the CTS
pin is used. As shown in
pin will normal ly be high,
and will be lo w whenever the m odem is able t o accept
new data. The CTS
pin will go high again a s soon as a
start bit is detected on the RXD pin and will remain high
until the modem is ready to accept another character.
Low Power Modes
The Si2400 has three low power modes. These are
described below:
!
DSP Powerdown. The DSP processor can be
powered down by setting register PDDE (SEB.3) =1.
In this mode the serial interface still functions as
normal, and the modem will be able to detect ringing
and intrusion. No modem modes or tone detection
features will function.
!
Wake Up On Ring. By issuing the “z” command, the
Si2400 goes into a low power mode where both the
microcontroller and DSP are powered down. Only
incoming ringing or a total reset will power up the
chip again.
!
Total Powerdown. By writing registers PDN (SF1.6)
and PDL (SF1.5), the Si2400 will be put into a total
powerdown mode. In this mode, all logic is powered
down, including the crystal oscillator and clock-out
pin. Only a hardware reset can restart the Si2400.
14Rev. 0.95
Si2400
Global DAA Operation
The Si2400 chipset co ntains an in tegrated sil icon direc t
access arrangement (silicon DAA) that provides a
programmable line interface to meet international
telephone line interface requirements. Table 13 gives
the DAA register setti ngs required t o meet internati onal
PTT standards. A detailed description of the r egisters in
Table 13 can be found in "Appendix A—DAA
Operation‚" on page 62.
Table 13. Country-Specific Register Settings
RegisterSF5SF7SF6
CountryOHSACTDCTRZRTLIMVOLFNM
Australia112 0000 0
Bulgaria 01200000
CTR21
Czech Republic012 0000 0
FCC002 0000 0
Hungary002 0000 0
Japan001 0000 0
Malaysia
New Zealand012 0000 0
Philippines001 00001
Poland
Singapore
Slovakia 01200000
Slovenia01200000
South Africa
South Korea
1
2
3
2
3
3
013 0010 0
001 0000 0
002 1100 0
001 0000 0
112 1000 0
001 1000 0
Note:
1. CTR21 includes the following countries: Austria, Belgium, Cyprus, Denmark, Finland, France,
Germany, Greece, Iceland, Ireland, Israel, Italy, Liechtenstein, Luxembourg, Netherlands, Norway,
Portugal, Spain, Sweden, Switzerland, and the United Kingdom.
2. Supported for loop current ≥ 20mA.
3. The RZ register (SF5.1) should only be set for Poland, South Africa and South Korea if the ringer
impedance network (C15, R14, Z2, Z3) is not populated.
Parallel Phone Detection
The Si2400 has the abilit y to detect another phone that
is off hook on a shared li ne. This all ows the ISO modem
both the ability to avoid interrupting another call on a
shared line and to intelligently handle an interruption
when the Si2400 is using the line. An automatic
algorithm to detect paralle l phone intrusion (defined as
an off-hook parallel handset) is provided by default.
On-Hook Intrusion Detection
The on-hook intrusion detection allows the user to avoid
interrupting another ca ll on a shared line. To implement
the intrusion detecti on, the Si2400 uses a loop vol tage
sense (register LVCS (SDB)). When on hook, LVCS
monitors the line voltage. ( When off hook, it measures
current.) LVCS has a full scale of 70 V with an LSB of
2.25 V. The first code (0 → 1) is skewed such that a 0
indicates that the line voltage is < 3.0 V. The voltage
accuracy of LVCS is ±20%. The user can read these
bits directly when on hook through register LVCS.
The automatic on-hook detector algorithm can be
tripped by either an absolute level or by a voltage
differential by selecting ONHD (S13.3). If the absolut e
detector is chosen, th e Si2400 algorithm will d etect an
intrusion if LVCS is less than the on-hook intrusion
Rev. 0.9515
Si2400
threshold, register AVL (S11.4:0). In other words, it is
determined that an intrusion has occurred if LVCS <
AVL.
AVL defaults to 0x0D, or 30 V on powerup. The
absolute detector is the co rrect method to use for FCC
and most other countries. T he absolu te detector sho uld
also be used to de tect the presence (or abs ence) of a
line connection.
Under the condition of a ver y short line and a currentlimiting telephone off hook, the off-hook line vo ltage can
be as high as 40 V. The minimum on-hook voltage may
not be much greater. This condition can occur on phone
30
25
20
LVCS
BIT
15
lines with current-li mi tin g s pec if ic ations s uch as Fra nce.
For these lines, a differential detector is more
appropriate.
The differential detector method checks the status of the
line every 26.66 ms. The detec tor compares (LVCS (t –
0.02666) – LVCS (t)) to the differential threshold level
set in register DVL (S11.7:5). The default for DVL is
0x02 (5.25 V). If the threshold is ex ceeded (LVCS (t –
0.02666) – LVCS (t) > D VL), an in trusion is detected. If
(LVCS (t) – LVCS (t – 0.02666) > DVL), then the
intrusion is said to have terminated.
10
5
0
0
36333027242118151293639424548
Loop Voltage
Figure 7. Loop Voltage—LVCS T ransfer Function
Off-Hook Intrusion Detection
When the Si2400 is off hook, it can detect another
phone going off hook by monitoring the DC loop current.
The loop current sense transfer function is shown in
Figure 8 with the upper curve representing CTR21
(current limiting) operation and the lower curve
representing all other modes. The overload points
indicate excessive current draw. The user can read
these bits directly through register LVCS (SDB). Note
that as in the line voltage sense, there is hysteresis
between codes (0.375 mA for CTR21 mode and
0.75 mA for ROW).
7269666360575451
100
16Rev. 0.95
Si2400
Overload
30
25
LCS
BIT
20
15
10
5
0
0
36333027242118151293639424548
CTR21
Loop Current (mA)
Figure 8. Loop Current—LVCS Transfer Function
The off-hook algorithm can be chosen to use eithe r a
differential current detector or an absolute current
detector via setting OFHD (S13.4).
Because of the extra code and host processing required
by the absolute current method, the differe ntial current
method is chosen to be the defau lt. This method uses
two techniques to detect an intrusion. The first
technique is described as follows:
If (LVCS (t – 400 ms) – LVCS (t)) > DCL, then an
intrusion is deem ed to have taken place. If (LVCS (t) –
L VCS (t – 400 ms)) > DCL, then the intrusion is deemed
to have completed. Default DCL is 2.
The second technique takes advantage of the DC
holding circuit. If a parallel phone suddenly goes off
hook, the DC holding circuit will not reac t immediately,
therefore the loop c urrent through the Si2400 will drop
briefly to zero. Thus, an i ntrusion is als o reported when
LVCS = 0.
If the absolute detector is chosen, the Si2400 will detect
an intrusion under the condi tion that LVCS is less than
the off-hook intrusion threshol d, regi ster A CL (S12.4: 0).
In other words, it is determined that an intrusion has
occurred if LVCS < ACL. ACL defaults to 3 (15.5 mA) on
powerup. Because the loop current can vary from
20 mA to 100 mA, depending on the line, a factory
preset threshold is not useful.
If the host wishes to use this absolute mode, the host
must measure the line current and then set the
threshold accordingly. A measurement of the loop
726966636057545175 78 81 84 87 90 93
140
current is accomplished by going off-hook (issuing the
“ATDT;” command), reading LVCS after 50 ms, and
going back on hook using the “ATH” command. This
measured value of LVCS should be used to determine
the threshold register ACL. If this method is used, the
loop current should b e measur ed on a pe riodic bas is to
account for drift in line resistance.
The absolute curren t method is the most accu rate, and
it is necessary to use thi s method in order to determ ine
if another phone goes off hook simultaneous with or
immediately (< 400 ms) af ter the Si 240 0 phon e goe s off
hook. It does, however, require processi ng by the host,
including periodic off-hook events to measure the loop
current.
If an intrusion event is detected while in command
mode, an “i” is echoed to the host; When it is terminated
an “I” is echoed. The host may also be notified of an
intrusion when in data mo de through the A LERT pin by
setting GPIO4 (SE2.7:6) = 3. Upon intrusion, the
ALERT pin will go high, and the host may then read
register IND (S14.1) to confirm an intrusion.
The host may use the automatic intrusion detection
algorithm (the default ) by monitoring the ALERT pin or
waiting for the character echoes. The host may also use
the LVCS, AVL, and DVL registers as a basis for a
custom algorithm. Note that LVCS only acts as a line
voltage sense when on hook. When off hook, it
becomes the line current sense register.
Rev. 0.9517
Si2400
Carrier Detect/Loss
The Si2400 can provide the functionality of a loss-ofcarrier pin similar t o the CD pin functionality in an R S232 connection. If programmed as an ALERT, GPIO4
will go high in online mod e when either parallel phone
intrusion or a loss-of- carrier is detected. When used in
this manner, the host detects a low-to-high trans ition on
GPIO4 (ALERT), escapes into command mode, and
reads register IND (S14.1). If high, IND indicates
intrusion. If low, IND indicates loss-of-carrier.
Overcurrent Protection
The Si2400 has built in prote ction to avoid damage to
the device due to overcurrent situations. An example
situation occurs when plugging the m ode m i nto a d igital
PBX outlet and attempting to go off-hook. Digital PBX
systems vary, but many can provide a DC feed vol tage
of up to 70 V and therefore have the ability to deliver
hundreds of milliamps of current into the DAA.
The Si2400 will always go off hook with the currentlimiting mode enabled. This allows no possibility of
damage for voltages up to about 48 V. However, at
higher voltages the 43 V Zener protection device will
begin to conduct and co uld be damaged if the power is
applied for too long.
The Si2400 will det ect the v alue of the lo op cur rent at a
programmable time after going off-hook (default =
20 ms) via register OHT (S32). If the loop current is too
high, an “x” will be echoed back to the host to indi ca te a
fault condition. The host may then check register OD
(S14.3) to confirm an overcurrent condition and go back
on hook if necessary.
The user can optionally enable another protection
feature, the overcurrent protection, via register AOC
(S14.4). This protection feature can automatically detect
an overcurrent condition and put the Si2400 into a lower
drive mode, which is si milar to the current-limi ting mod e
but has reduced hoo kswitch drive. This feature allows
the Si2400 to remain off-hook on a digital line for a
longer period of time without damage. If the Si2400
does not detect over current aft er the time s et by OCDT
(S32), then the c orrect line terminat ion is applied. This
method of going off hook in current-limiting mode can
be disabled by clearing OFHE (S13.5).
Caller ID Decoding Operation
The Si2400 supports ful l cal le r ID d etecti on a nd dec od e
for US Bellco re, UK, and Japanese standards. To use
the caller ID decoding feature, the following set-up is
necessary:
1. Set ND (SEO.3) = 0 (Set modem to 8N1 configuration)
2. Set CIDU (S13.1) = 1(Set modem to Bellcore type caller
ID) or CIDB (S13.2) = 1 (Set modem to UK type caller ID)
or JID (S13.7) = 1 (Set modem to Japanese type caller ID)
3. Set baud rate either to 1200 bps without flow control or
greater than 1200 bps with flow control.
Bellcore Caller ID Operation
The Si2400 will d etect the fir st ring burst sig nal and will
echo an “R” to the host. The device will then start
searching for the call er ID preamb le sequen ce after the
appropriate time-out. When 50 continuous mark bits
have been detected, the “m” res pon se will be ec hoe d to
indicate that the mark has been detected and that caller
ID data will follow.
At this point the algorith m will look for the first start bi t,
assemble the characters, and then transmit them out of
the UART as they are detected. When the caller ID
burst finishes, the carrier will be lost and the modem will
echo an “N” to indicate that the carrier is lost.
At this point the Si2400 will continue detecting ring
bursts and echoing “R” for each burst, and will
automatically answer after the correct number of rings.
UK Caller ID Operation
When the Si2400 detect s a line reversa l, it will echo an
“f” to the host. It will then start searching for the Idle
State Tone Alert Signal. When this signal has been
detected, the Si2400 will transmit an “a” to the host.
After the Idle State Tone Alert Signal is completed, the
Si2400 will apply the wetting pulse for the required
15 ms by quickly going o ff hook and o n hook . From th is
point on, the algorithm is identical to that of B ellcore in
that it will search f or the chan nel seizu re signal and the
marks before echoing an “m” and will then report the
decoded caller ID data.
Japan Caller ID Operation
After a polarity reversal and the first ring burst are
detected, the Si2400 is taken off hook. After 40 1s
(marks) have been det ected, the Si24 00 will search for
a start bit, echo an “m” for mar k, and begin asse mbling
characters and tra nsmitting them out through the s erial
port. When the carrier is lost, the Si2400 immediately
hangs up and echoes “N” . Al so, if no ca rrie r is d etecte d
for three seconds, the line hangs up and echoes “N”.
Force Caller ID Monitor
The Si2400 may be used to continuously monitor the
phone line for the caller ID mark signal s. This can be
useful in systems that require dete cti on of calle r ID data
before the ring sign al, voice mail indic ator signals, and
Type II caller ID support. To force the Si2400 into caller
ID monitor mode, set CIDM (S0C.5).
18Rev. 0.95
Si2400
Tone Generation and Tone Detection
The Si2400 provides comprehensive and flexible tone
generation and detection. This includes all tones
needed to establish a circuit connection and to se t up
and control a communication session. The tone
generation furnishes the DTMF tones for PSTN auto
dialing and the supervisory tone s for cal l establi shmen t.
The tone detection provides support for call progress
monitoring. The detect or can a lso be user- programme d
to recognize up to 16 DTMF tones and two tone
detection bandpass filters.
DTMF tones may be dete cted and generated by using
the “ATA0” and “AT!0” c ommands described in the AT
command section. A description of the userprogrammable tones can be found in "Modem Result
Codes and Call Progress‚" on page 30.
PCM Data Mode
The Si2400 has the ability to bypass the modem
algorithm and send 14-bit PCM data, sampled at
9600 Hz, across the DAA. To use this mode, it is
necessary to set the serial link baud rate to at least
228613 bps (SE0), set PCM (S13.0) = 1, and set MCKR
(E1.7:6) = 0. The data format (Figure 9) requires that
the high byte be sent first contain ing bits D13–D7. The
LSB (B0) must e qual zero. The low by te must be sent
next containing bits D6–D0; the LSB (B0) must equal
one. The receive data format is the same.
In PCM data mode, the line can be answ ered using th e
“ATA;” command or a call can be origina ted using the
“A TDT#;” command. (The “;” is used to keep the modem
from leaving the command mode.) When PCM data
mode is enabled (set PCM (S13.0) = 1 and DRT
(SE4.5:4) = 0 (default)), data will immediately begin
streaming into and out of the serial port at a 9600 H z*2
word rate. In this mode, the controller will not detect dial
tones or other ca ll progress tones. If desi red, the user
can monitor these tones using manual call progress
detection prior to entering the PCM data mode.
To exit the PCM data mode, an escape must be
performed either by p ulsing the ES C pin or by using 9bit data mode and setting th e ninth bit. (TIES c annot b e
used in PCM data mode.) The escape command will
disable PCM streaming, and the controller will again
accept AT style commands.
Note: PCM data mode is the format that must also be used
when the Si2400 is configured to run as a voice codec
(DRT = 3).
PCM Receive Timing
8-Bit Data
TXD
Start
D7D8D9D10D11D12D13D0D1D2D3D4D5D6
B0
B1
B2B3B4B5B6B7
High-Byte
Stop
Start
Low-Byte
B0
B1B2B3B4B5B6B7
PCM Transmit Timing
8-Bit Data
RXD
StartB1
Note: Baud rates (programmed through register SE0) can be set to the following: 228613, 245760, and 307200.
D7D8D9D10D11D12D13D0D1D2D3D4D5D6
B0
High-Byte
B2B3B4B5B6B7
Stop
Start
Low-Byte
B0
B1B2B3B4B5B6B7
Figure 9. PCM Timing
Stop
Stop
Rev. 0.9519
Si2400
A.
TX
RX
RXD
TXD
DSP
DSPOUT
DSPIN
Data Mode (DRT = 0)
Si2400
Si3015
RJ11
RJ11
B.
C.
TX
RX
TX
RX
RXD
TXD
RXD
TXD
DSP
DSPOUT
DSPIN
DSP
DSPOUT
DSPIN
AOUT
(Call Progress)
Voice Mode (DRT = 1)
Si2400
AIN
AOUT
(Voice Out)
(Voice In)
Loopback Mode (DRT = 2)
Si2400
AIN
Si3015
RJ11
RJ11
AIN
AOUT
Codec Mode (DRT = 3)
Si2400
DSP
RXD
TX
D.
20 Rev. 0.95
RX
TXD
DSPOUT
DSPIN
AIN
AOUT
(Voice Out)
Figure 10. Signal Routing
AIN
Si3015
RJ11
AIN
(Voice In)
Si2400
Analog Codec
The Si2400 features an on-chip, voice quality codec.
The codec consists of a digital to analog converter
(DAC) and an analog to digital converter (ADC). The
sample rate for the codec is set to 9.6 kHz. Wh en the
codec is powered on (s et register APO (SE 4.1)=1), the
output of the DAC is always present on the Si2400
AOUT pin. When the c ode c is po wer ed off (APO = 0), a
PWM output is present on the AOUT pin instead. In
order to use the ADC , one of the four GPIO pins must
be selected as an analog input ( AIN) by programming
the GPIO register (SE2).
Figure 10 shows the various signal routing modes for
the Si2400 voice codec, which are programmed through
register DRT (SE4.5:4). Figure 10A shows the data
routing for data mode. This is the default mode, which is
used for the modem data forma ts. In this configurat ion,
AOUT produces a mixed sum of the DSPOUT and
DSPIN signals and is typically used for call progress
monitoring through an external speaker. The relative
levels of the DSPOUT and DSPIN signals that are
output on the AOUT pin can be set through registers
ATL (SF4.1:0) and ARL (SF4.3:2).
Figure 10B shows the format for sending analog v oice
across the DAA to the PSTN. AIN is routed directly
across the DAA to the telephone line. In this
configuration, AOUT produces a mixed sum of the
DSPOUT and DSPIN signals . The relative levels of the
DSPOUT and DSPIN signals that are output on the
AOUT pin can be set through registers ATL (SF4.1:0)
and ARL (SF4.3:2). Note that the DSP may process
these signals if i t is not in PCM data mode. Thus, th e
DSP may be used in this configuration, for exam ple, to
decode DTMF tones. This is the mode used with the “!0”
and “A0” commands.
Figure 10C shows the loopback format, which can be
used for in-circuit t esting. A detailed description of the
in-circuit test modes is des cribed in the "Appendix A—
DAA Operation‚" on page 62.
Figure 10D shows the codec mode. This format is
useful, for example, in voice prompting, speaker
phones, or any systems involving digital signal
processing. In this mode, DSPOUT is routed to both the
AOUT pin and to the telephone li ne, and AIN is routed
directly to DSPIN.
Note that in all the DRT formats, the DSP must be in
PCM mode in order to pass DSPIN and DSPOUT
directly to and from TXD and RXD.
V.23 Operation/V.23 Reversing
The Si2400 supports full V.23 operation including the
V.23 reversing procedure. V.23 operation is enabled by
setting MF8 (S07) = xx10xx00 or xx01xx00. If V23R
(S07.5) = 1, then the Si2400 will transmit data at 75 bps
and receive data at either 600 or 1200 bps. If V23T
(S07.4) = 1, then the S i2400 will receive da ta at 75 bps
and transmit data at either 600 or 1200 bps. BAUD
(S07.2) is the 1200 or 600 bps ind icator. BAUD = 1 will
enable the 1200/600 V.23 channel to run at 1200 bps
while BAUD = 0 will enable 600 bps operation.
When a V.23 connection is successfully established, the
modem will respond with a “c” character if the
connection is made with the modem transmitting at
1200/600 bps and receivi ng at 75 bps. The m odem will
respond with a “v” character if a V.23 connection is
established with the modem transmitting at 75 bps and
receiving at 1200/600 bps.
The Si2400 supports a V.23 turnaround procedure. This
allows a modem th at is tran smitting at 75 bps to init iate
a “turnaround” procedure so that it can begin
transmitting data at 1200/600 bps an d receiv ing data a t
75 bps. The modem is define d as being in V.23 master
mode if it is transmi tting at 75 bps and it is defi ned as
being in slave mode if the modem is transmitting at
1200/600 bps. The f ollowi ng pa ra gr aph s gi ve a d etai le d
description of the V.23 turnaround procedure.
Modem in master mode
To perform a direct turnaround once a modem
connection is established, the host goes into onlinecommand-mode by sending an escape command
(Escape pin activation, TI ES, or ninth bit esc ape) to the
master modem. (Note that the host can initiate a
turnaround only if the Si2400 is the master.) The host
then sends the ATRO command to the Si2400 to initiate
a V.23 turnaround and to go bac k to the online (data)
mode.
The Si2400 will then change its carrier frequency (from
390 Hz to 1300 Hz), and wait for detecting a 390 Hz
carrier for 440 ms. If the modem detects more than
40 ms of a 390 Hz carrier into a time window of 440 ms,
it will echo the “c” response character. If the modem
does not detect more than 40 ms of a 390 Hz carrier
into a time window of 44 0 ms, it will hang up and ech o
the “N” (no carrier) character as a response
Modem in slave mode
The Si2400 performs a reverse turnaround when it
detects a carrier drop longer than 20 ms. The Si2400
then reverses (it changes its carrier from 1300 Hz to
390 Hz) and waits to detect a 1300 Hz carrier for
220 ms. If the Si2400 detects more than 40 ms of a
Rev. 0.9521
Si2400
1300 Hz carrier in a time window of 22 0 ms, then it will
set the ALERT pin (GPIO4 must be configured as
ALERT) and the next charac ter echoed by the Si2400
will be a “v”.
If the Si2400 does not detect more than 40 ms of the
1300 Hz carrier in a time window of 220 ms, then it
reverses again and waits to detect a 3 90 Hz carrier for
220 ms. Then, if the Si2400 detec ts mo re than 40 ms of
a 390 Hz carrier in a time window of 220 ms, it will set
the ALERT pin and the next character echoed by the
Si2400 will be a “c”.
At this point, if the Si2400 does not detect more than
40 ms of the 390 Hz carrier in a time window of 220 ms,
then it will hang up, set the ALERT pin, and the next
character echoed by the Si2400 will be an “N” (no
carrier).
Successful completion of a turnaround procedure in
either master or slave will automatically update V23T
(S07.4) and V23R (S07 .5) to indicate the new statu s of
the V.23 connection.
In order to avoid using the ALERT pin, the host may
also be notified of t he ALERT condition by using 9-bit
data mode. Setting NB E (S15.0) = 1 a nd 9BF (C .3) = 0
will configure the ninth bit on the Si2400 TXD path to
function exactly as the ALERT pin has been described.
V.42 HDLC Mode
The Si2400 supports V.42 through HDLC framing in
hardware in all modem data modes. Frame packing and
unpacking, including opening and closing flag
generation and detection, CRC computation and
checking, zero inse rtion and deletio n, and modem data
transmission and reception are all performed by the
Si2400. V.42 error correction and data compression
must be performed by the host.
The digital link interface in this mode uses the same
UART interface (8-Bit Data and 9-Bit Data formats) as in
the asynchronou s modes and the nin th data bit may b e
used as an escape b y setting NBE (S15.0) = 1. When
using HDLC in 9-Bit Data mode, if the ninth bit is not
used as an escape, it is ignored.
To use the HDLC feature on the Si2400, the hos t must
first enable HDLC operation by setting HDEN
(S07.7) = 1. Next, the host may initiate the call or
answer the call using either the “ATDT#”, the “ATA”
command, or the auto- answer mode . (The auto -answer
mode is implemented by se tting register NR (S0) to a
non-zero value.) When the call is connected, a “c”, “ d”,
or a “v” is echoed to the host controller. The host may
now send/receive data across the UART using either
the 8-Bit Data or 9-Bit Data formats with flow control.
At this point, the Si24 00 will begin framing da ta into the
HDLC format. On the transmit side, if no data is
available from the host, the HDLC flag pattern is sent
repeatedly. When data is available, the Si2400
computes the CRC code throughout the frame and the
data is sent with the HDLC zero-bit insertion algorithm.
HDLC flow control operates in a similar manner to
normal asynchronous flow control across the UART and
is shown in Figure 11. In order to operate flow control
(using the CTS
pin to indicate when the Si2400 is ready
to accept a character), a higher serial link baud rate
than the transmission line rate should be selec ted. The
method of transmitting HDLC frames is as follows:
1. After the call is connected, the host should begin sending
the frame data to the Si2400, using the CTS
ensure data synchronicity. A 1-deep character FIFO is
implemented in the Si2400 to ensure that data is alway s
available to transmit.
2. When the frame is complete, the host should simply stop
sending data to th e Si240 0. As sho wn i n Figure11B, since
the Si2400 does not yet recognize the end-of-frame, it will
expect an extra byte and assert CTS
cause a host interrupt, then this final interrupt should be
ignored by the host.
3. When the Si2400 is ready to send the next byte, if it has
not yet received any data from the host, it will recognize
this as an end-of-frame, raise CTS
code, transmit the code, and begin transmitting stop flags.
4. After transmitting the first stop flag, the Si2400 will lower
CTS indicating that it is ready to receive the next frame
from the host. At this point the process repeats as in
step 1.
, calculate the final CRC
flow control to
. If CTS is used to
The method of receiving HDLC frames is as follows:
1. After the call is connected, the Si2400 searches for flag
data. Then, once the first non-flag word is detected, the
CRC is continuously computed, and the data is sent
across the UART (8-Bit Data or 9-Bit Data mode) to the
host after removing the HDLC zer o-bi t in sertio n. The baud
rate of the host must be at least as high as that of data
transmission. HDLC mode only works with 8-bit data
words; the ninth bit is used only for escape on RXD and
EOFR on TXD.
2. When the Si2400 detects the stop flag, it will send the last
data word in the frame as well as the two CRC bytes and
determine if the CRC checksum matches or not. Thus, the
last two bytes are not frame data, but are the CRC bytes,
which can be discarded b y the host. If the checksum
matches, then the Si2400 echoes “G” (good). If the
checksum does not match, the Si2400 echoes “e” (error).
Additionally, if the Si2400 detects an abort (seven or more
contiguous ones), then it will echo an “A”.
When the “G”, “e”, or “A” (referred to as a frame result
word) is sent, the Si2400 raises the EOFR (end of frame
receive) pin (see Figure 10B). The GPIO1 pin must be
configured as EOFR by setting GPE (SE4.3) = 1. In
addition to using the EOFR pin to indicate that the by te is a
22Rev. 0.95
Si2400
frame result word, if in 9-bit data mode (se t NBE (S15.0) =
1), the ninth bit will be raised if the byte is a frame result
word. To program this mode, set 9BF (S0C.3) = 1 and ND
(SEO.3) = 1.
3. When the next frame of data is detec ted, EOFR is low ered
and the process repeats at step 1.
To summarize, the host will begin receiving data
asynchronously from the Si2400. When each byte is
received, the host sh ould check the EOFR pin (or the
ninth bit). If the pin (or the ninth bit) is low, then the data
is valid frame data. If the pin (or the ninth bit) is high,
then the data is a frame result word.
Fast Connect
In modem applications that require fast connection
times, it is possible to expedite the handshaking by
bypassing the answer tone. The No Answer Tone (NAT)
bit (S33.1) is intende d to provid e a method to decreas e
the time needed to complete modem handshaking. If
the NAT bit is set, the Si2400 will bypa ss transmi tting a
2100 Hz or 2225 Hz ans wer tone whe n recei ving a call .
Instead, the modem will immediately begin the
handshaking sequence that normally follows answer
tone transmission. For example, when the modem is
configured as a V.22 answering modem, activating the
NAT bit will cause the mod em to immediately transmit
unscrambled ones at 1200 bps after the modem
connects to the line. In addition, register UNL (S20) may
be used to set the length of time that the modem
transmits unscrambled ones. Setting UNL to a value
lower than the default may also shorten the answer
sequence.
When the modem is set up to originate a call, setting the
NAT bit causes the modem to bypass the normal
answer tone search . Instead, the modem will sen d the
transmit sequence t hat normally occurs after receiv ing
the answer tone within 20 ms of th e start of the answ er
tone. For example, when the m odem is config ured as a
V.22 originating modem, activating the NAT bit will
cause the modem to start transmi tting scrambled ones
at 1200 bps within 20 ms of the start of an answer tone.
When NAT=0, additional modem handshaking control
can be adjusted through registers TATL (S1E), ATTD
(S1F), UNL (S20), TSOD (S21), TSOL (S22), VDDL
(S23), VDDH (S24), SPTL (S25), VTSO (S26), VTSOL
(S27), VTSOH (S28), RSO (S2A), FCD (S2F), FCDH
(S30), RATL (S31), TASL (S34), and RSOL (S35).
These registers c an be esp ecially us eful if t he user has
control of both the originating and answer modems.
Clock Generation Subsystem
The Si2400 contai ns an on-chip cl ock generator. Using
a single master clock input, the Si2400 can genera te all
modem sample rates necessary to support V.22bis,
V.22/Bell212A, and V.21/Bell103 standards as well a s a
9.6 kHz rate for audio playback. Either a 4.9152 MHz
clock on XTALI or a 4.9152 MHz crystal ac ross XTALI
and XTALO form the master clock for the S i2400. This
clock source is sent to an internal phase-locked loop
(PLL) which generates all necessary internal system
clocks. The PLL has a settlin g time of ~1 ms. Data on
RXD should not be sent to the dev ice pri or to se ttling of
the PLL.
A CLKOUT pin exists whereby a 78.6 432 MHz /(N + 1)
clock is produced which may be used to clock a
microcontroller or other devices in the system. N may
be programmed via CLKD (SE1.4:0) to any value from 1
to 31, and N defaults to 7 on power-up. The clock may
be stopped by setting N = 0.
The MCKR (microc ontroller clock rate r egister SEI.7:6)
allows the user to co ntrol the m icrocontrol ler cloc k rate.
On powerup, the Si2400 UART baud rate is set to
2400 bps, given that the clock inp ut is 4.91 52 MH z. Th e
MCKR register conserves power via slower clocking of
the microcontroller for specific applications where
power conservation is required. Table 14 shows the
configurations for different values of MCKR.
Note that if MCKR = 0, then all of the serial interface link
rates will run at either half (MCKR = 1) or quarter
(MCKR = 2,3) speed.
Table 14. MCKR Configurations
MCKRModes Working
0
(9.8304 MHz)
1
(4.9152 MHz)
2,3
(2.4576 MHz)
All modes
All modes except
PCM streaming
and V22bis
Command modes
only
Rev. 0.9523
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