AS2540Q

D ata Sheet AS2540 austria micro systems austriamicrosystems DATA SHEET (PRELIMINARY) Remote Controlled Single-Chip-Telephone AS2540 General Description The AS2540 is a CMOS integrated circuit that incorporates a speech circuit (line-adaptation, 2/4-wire conversion, separate Rx- and Tx-amplifiers for handset and modem), MF dialler, ring frequency detector, ring melody generator and a two wire serial interface. It shall act as an a/b-line-powered device in order to interface a main-powered CPU to the analogue telephone line. AS2540 can operate in a so-called mainpower mode and in a backup mode. During mainpower mode, a watchdog timer is running on AS2540, which has to be reset via the serial interface, which is connected to the CPU through opto-couplers. During backup mode (= The main-power failure or SW engine problem), AS2540 can operate as an independent basic MF dialler (digits 0-9*#) Key Features - L ine Interface, Speech Circuit, MF Dialler and Tone Ringer on a 28 pin CMOS chip P rogrammable via 2-wire serial interface (UART 9600 baud, 8N1) W atch dog timer for Backup Mode A dditional input for modem transmit path A dditional output for modem receive path C MOS for high EMC immunity L ow Noise (max. –72 dBm) O perating range from 15mA to 100mA (down to 5mA with reduced performance) S oft clipping for handset operation to avoid harsh distortion L ine loss compensation selectable by pin option R eal and complex impedance selectable by external components S ide tone adaption selectable by external components R ing frequency discrimination 3 -tone ring melody generator Applications - W eb Telephones A nswering Machines F ax Machines B ase Station of Cordless Telephones H ospital Communication Units Package - 2 8 pin SOIC D ice-on-Foil Block Diagram Main Power Mode Line LS LI + 6dB Backup Mode Line LS LI + 6dB RI SB T -2d B + 2d B ROH ROT M1 M2 RI SB T -2dB + 2d B ROH ROT M1 M2 CS Mask CS Mask T IT CI DPn DT MFgenerator T IT CI AGND DPn DT MFg enerator AGND SMUT E S MASK S MAS K SMUTE SROH SROH SROT S DPn S DPn Dia l Dig it Dial Digit ST IT SROT ST IT RxD RxD DIALLER C1 C2 C3 R1 R2 MODE UART T xD C1 C2 C3 R1 R2 MODE VDD DIALLER UART T xD VDD RFD MO EHS MHS VS S OS C RFD MO EHS MHS VS S OSC Revision 3.1 Page 1 of 18 D ata Sheet AS2540 austria micro systems Pin Description Pin # 15 Symbol RFD Function R ing F requency D iscrimination Schmitt trigger input for ring frequency discrimination. Disabled during off-hook. 7 LS L ine Current S ense Input Input for sensing the line current 5 LI L ine I nput Input used for power extraction and line current sensing 6 RI R eceive I nput Input for ac-separated receive signal 2 STB S ide T one B alance Input Input for side tone cancellation network 3 CS C urrent S hunt Control Output N-channel open drain output to control the external high power shunt transistor for synthesising ac- and dc- impedance, modulation of line voltage and shorting the line during make periods of pulse dialling 8 CI C omplex I mpedance Input Input pin for the capacitor to program a complex impedance 16 DPn D ial P ulse Output Open drain output pulls low during break periods of pulse dialling and flash 17 EHS E lectronic H ook S witch Schmitt Trigger Input to detect an electronic off-hook. 18 MHS M anual H ook S witch Schmitt Trigger Input to detect a manual off-hook. 19 MODE D TMF L evel S election -4/-6dBm -6/-8dBm -8/-10dBm —> —> —> DLS open DLS-r1 DLS-r2 L ine L oss C ompensation Select Pin 45mA-75mA 20mA-50mA None 28 MO Ring —> —> —> LLC open LLC-r3 LLC-r4 M elody O utput PDM output of the ring melody generator. 11 VDD V oltage D rain D rain Positive Power Supply 4 VSS V oltage S ource S ource Negative Power Supply Revision 3.1 Page 2 of 18 D ata Sheet AS2540 austria micro systems Pin # 25 Symbol OSC Function O scillator Input Input for ceramic resonator 3.58MHz. Recommended type: Murata CSA 3.58MG312AM or compatible 12 AGND A nalogue G round Special ground for the internal amplifiers 26 RXD R eceive D ata Input Schmitt trigger input to serial interface 27 TXD T ransmit D ata Output Open drain output from serial interface Keyboard Keyboard 20 21 22 23 24 10 R1 R2 C1 C2 C3 ROT R ows C olumns R eceive O utput to T ransformer Output for driving a transformer with an ac impedance larger than 10k Ω 1 TIT T ransformer I nput from T ransformer Single ended input for transformer 9 ROH R eceive O utput to H andset Output for driving a dynamic earpiece with an impedance from 150 Ω t o 300 Ω 13 14 M2 M1 M icrophone Inputs Differential inputs for the microphone (electret) Revision 3.1 Page 3 of 18 D ata Sheet AS2540 austria micro systems Functional Description Modes of operation There are 4 possible modes: Example Main Power Mode Line LS LI + 6dB RI ST B -2dB + 2dB ROH ROT M1 M2 Idle Mode Manual hook-switch and electronic hook-switch (e.g. relay) is open (MHS ∩ E HS = logical 0), no ring signal is applied, the oscillator is stopped, signalling via the serial interface is not possible. CS Mask T IT CI DP n DT MFgenerator AGND S MAS K SMUT E SROH S DPn Dial Digit Ringing Mode AS2540 is supplied via the ring capacitor and external path, manual hook -switch and electronic hook-switch is open (MHS ∩ E HS = logical 0), the oscillator is running, a valid incoming ringing is signalled via the serial interface to the CPU. If the CPU does not reply the AS2540 switches into backup mode and sends a ring melody to the MO output. C1 C2 C3 R1 R2 MODE SROT ST IT RxD DIALLER UART T xD VDD RFD MO EHS MHS VS S OS C Backup Mode Manual hook-switch and/or electronic hook-switch is closed (MHS ∪ E HS = logical 1), AS2540 is supplied with line current, the oscillator is running, the keyscan is enabled and the handset path is switched on, signalling via the serial interface is possible. After AS2540 has started dialling in backup mode, he must not be interrupted any more in order to ensure consistent dialling. A mode transition BM -> MPM is only possible before AS2540 has started dialling digits independently. Start-up in backup mode As soon as AS2540 is supplied with line current, the external V dd c apacitor will be charged up via the LI and VDD pin and after the V dd v oltage has reached the operating level, the handset path of the speech circuit is switched on. This off-hook status is also signalled to the internal logic via the MHS or EHS pin in order to start the pinscan and subsequently set the country specific modes. Additionally a message is sent to the CPU. Start-up in ring mode When a ringing signal is applied to the line, V dd o f AS2540 is charged up via an external path. After V dd h as reached the operating voltage the oscillator starts and AS2540 discriminates the ring frequency. After a valid ring frequency is applied on the RFD pin, the logic sends a message is sent to the CPU and a watchdog timer is started. When the message is not quit by the CPU before the watchdog timer has finished the countdown, AS2540 changes into backup mode and sends out a melody via the MO pin. Main Power Mode Manual hook-switch and/or electronic hook-switch is closed, AS2540 is supplied with line current (MHS ∪ E HS = logical 1), the oscillator is running, the keyscan is disabled, AS2540 is controlled via the serial interface, handset path or monitor path or modem path is on, signalling via the serial interface is possible. Select Operation Mode Command Message Switches ON SROH SROT & STIT SROH & SROT Switches OFF SROT & STIT STIT DC conditions The normal operating mode is from 15mA to 100mA. An operating mode with reduced performance is from 5mA to 15mA. In the line hold range from 0mA to 5mA the device is in a power down mode and the voltage at LI is reduced to a maximum of 3.5V Revision 3.1 Page 4 of 18 D ata Sheet AS2540 austria micro systems Receive path The gain of the LS —> ROH receive path is set to 2dB for ac-impedance 1000 Ω . The receive input is the differential signal of RI and STB. During DTMF dialling a MF comfort tone is applied to ROH which is -30dB relative to the line level. The soft clip circuit limits the output voltage at ROH to 1V p. I t prevents harsh distortion and acoustic shock. The gain of the LS —> ROT receive path is set to 0dB for ac-impedance 1000 Ω . The receive input is the differential signal of RI and STB. The soft clip circuit is not active for this output. The DC characteristic is determined by the voltage at LI pin and a 30 Ω r esistor between LI and LS pin. It can be calculated by the following equation: V LS = V LI + I Line * 30 Ω . The t.m. voltage at the LI pin is 4.5V. The calculation leads to the following DC resistances: 330 Ω t o 75 Ω a t line currents from 15mA to 100mA. 2/4 wire conversion AS2540 has a built-in dual Wheatstone bridge with one common ground. This provides a maximum of independence of AC impedance and side tone from each other. One can adapt side tone without changing the AC impedance. Modescan The DTMF-level on the line and the function of the line loss compensation can be selected with the connection of the MODE-pin to the keyboard matrix. The MODE-pin is scanned once after each OFF-Hook transition. PIN MODE PIN C1 PIN C2 PIN C3 A1=3.4/3.5 A2=-0.4 R1 AC impedance The ac impedance of AS2540 is set to t.m. 1000 Ω . With the external capacitor at CI pin it can be programmed complex. With a parallel impedance at the LS pin it can be programmed to 600 Ω . R2 1 4 7 * c1 2 5 8 0 C2 3 6 9 # C3 PIN R1 PIN R2 Side Tone A good sidetone cancellation can be achieved by using the following equation: Z BAL /Z LIN E = 1 0 X X C3 C2 C1 R2 R1 LLC 45mA-75mA 45mA-75mA 45mA-75mA 20mA-50mA 20mA-50mA X X The gain of the TIT —> LS transmit path is set to 8dB for ac-impedance 1000 Ω . The input is single ended with an impedance of 25k Ω . The soft clip circuit is not active for this input. The dynamic range of this path is 2.5Vp at LS. X X X X X X X 20mA-50mA No LLC No LLC No LLC Dtmf Level -6dBm -8dBm -10dBm -6dBm -8dBm -10dBm -6dBm -8dBm -10dBm Transmit path The gain of the M1/M2 —> LS transmit path is set to 38dB for ac-impedance 1000 Ω . The input is differential with an impedance of 25k Ω . The soft clip circuit limits the output voltage at LS to 2V p. T he attack time is 30µs/6dB and the decay time is 20ms/6dB. X X X X indicates connection to pin mode Revision 3.1 Page 5 of 18 D ata Sheet AS2540 austria micro systems Serial interface The communication principle is derived from a standard UART: B aud Rate 9600 S tart Bit 1 D ata Bits 8 P arity None S top Bit 1 L SB is transferred prior to MSB Rx - messages Message Format X MSB X d5 d4 d3 d2 d1 1 LSB d7 x x x x x x x x x x x x x x x x x d6 x x x x x x x x x x x x x x x x x d5 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 d4 1 0 0 0 0 0 0 0 1 1 1 0 1 1 1 1 0 d3 0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 0 d2 1 0 1 1 0 0 1 1 0 0 1 0 0 0 1 1 0 d1 0 1 0 1 0 1 0 1 0 1 1 0 0 1 0 1 0 d0 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 DTMF-dial message Digit 0 Digit 1 Digit 2 Digit 3 Digit 4 Digit 5 Digit 6 Digit 7 Digit 8 Digit 9 Digit * Digit # Digit A Digit B Digit C Digit D KeyReleased Notes Starts DTMF dialling of digit Starts DTMF dialling of digit Starts DTMF dialling of digit Starts DTMF dialling of digit Starts DTMF dialling of digit Starts DTMF dialling of digit Starts DTMF dialling of digit Starts DTMF dialling of digit Starts DTMF dialling of digit Starts DTMF dialling of digit Starts DTMF dialling of digit Starts DTMF dialling of digit Starts DTMF dialling of digit Starts DTMF dialling of digit Starts DTMF dialling of digit Starts DTMF dialling of digit Stops Dialling d7 x x x x d6 x x x x d5 1 1 1 1 d4 0 0 0 0 d3 1 0 0 0 d2 1 0 1 1 d1 0 1 0 1 d0 1 1 1 1 Pin-Control message SetDPn_HIGH SetDPn_LOW SetMask ResetMask Notes Release pin Dpn (open drain) Force pin DPn = VSS Force LI-Voltage to 1.2 V Revision 3.1 Page 6 of 18 D ata Sheet AS2540 austria micro systems d7 x x x d7 x x x x x x x x d6 x x x d6 x x x x x x x x d5 1 1 1 d5 1 1 1 1 1 1 1 1 d4 0 0 0 d4 1 1 1 1 1 1 1 1 d3 1 1 1 d3 0 1 0 0 0 1 1 1 d2 1 0 0 d2 0 0 1 0 1 0 1 1 d1 1 0 1 d1 1 1 0 0 1 0 0 1 d0 1 1 1 d0 1 1 1 1 1 1 1 1 Pin-Control message SetTestmode MuteON MuteOFF Path-Control message SetHandsetPath SetMonitorPath SetModemPath RequestStatus reserved reserved reserved reserved Notes FOR FACTORY TEST ONLY Mute Transmit path Notes AS2540 sends Status information Tx messages message message format for b7 MSB b6 b5 b4 b3 b2 0 1 LSB b7 1 0 b6 b5 b4 b3 b2 b1 0 0 b0 1 1 1 1 1 1 1 1 1 1 1 1 1 Status valid ring signal detected no ring signal manual hook switch - off-hook (pin MHS) manual hook switch - on-hook (pin MHS) electronic hook switch - off-hook (pin EHS) electronic hook switch - on-hook (pin EHS) no LLC comparator ..................... LLC comparator 20mA (45mA) ... LLC comparator 26mA (51mA) ... LLC comparator 32mA (57mA) ... LLC comparator 38mA (63mA) ... LLC comparator 44mA (69mA) ... LLC comparator 50mA (75mA) ... Remark 1 0 1 0 0 0 0 0 1 1 1 0 0 1 1 0 0 1 0 1 0 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 Status of AS2540 coded status of LLC comparator Revision 3.1 Page 7 of 18 D ata Sheet AS2540 austria micro systems Message message format b7 MSB b6 b5 1 1 1 1 1 LSB b7 1 0 b6 b5 b4 1 1 b3 1 1 1 1 1 1 b2 1 1 1 1 1 1 b1 10 10 10 10 10 10 b0 1 1 1 1 1 1 Status valid ring signal detected no ring signal manual hook switch - off-hook (pin MHS) manual hook switch - on-hook (pin MHS) electronic hook switch - off-hook (pin EHS) electronic hook switch - on-hook (pin EHS) Remark 1 0 1 0 1 1 1 1 Status of AS2540 Protocol Line Events AS2540 has 3 inputs, namely MHS (Manual Hook Switch), EHS (Electronic Hook Switch) and RFD (Ring Frequency Detector), which sense the state of the two hook-switches and discriminate an applied ring signal. The MHS is connected to the manual hook switch which is operated by the handset and the EHS is connected to an electronic hook switch which is operated by the CPU. Whenever the state of these inputs changes, AS2540 immediately sends to the CPU after a debounce time. MHS and EHS up-debouncing lasts 15ms, down-debouncing lasts 85ms. RFD start to discriminate the ring frequency immediately but will send a message with a delay of 102ms. A status change of MHS and EHS pins must not change the momentary selected path of the speech network. The -message is sent without consideration of the momentary activities of AS2540 in order to meet PTT requirements (e.g. line break signalling). The code for the -message is chosen with regard to the minimum current consumption in order to operate the optocouplers. Pending -messages will be queued after the -message. An already running transmissions of will not be interrupted and will be sent afterwards in this case. M ode transitions Idle → B M → M PM → I dle AS2540 always starts up in backup mode and is prepared to act like an independent dialler. is sent to the CPU and AS2540 remains in back-up mode until any - valid message is sent from the CPU. This makes sure that a non-operable CPU does not disable basic dialling functions. - M ode transition MPM → B M A watchdog timer is started after and is reset whenever AS2540 receives a message from the CPU via the serial interface. If the CPU does not send any further valid message within 2400ms, AS2540 goes back into back-up mode, immediately locks the UART and remains in backup mode till next on-hook. Dialling Functions DTMF The DTMF generator provides 8 frequencies (in Hz): 1 1 697+1209 2 2 697+1336 3 3 697+1477 4 4 770+1209 5 5 770+1336 6 6 770+1477 7 7 852+1209 8 8 852+1336 9 9 852+1477 ** 941+1209 0 0 941+1336 # # 941+1477 Revision 3.1 Page 8 of 18 D ata Sheet AS2540 austria micro systems The MF output levels are set to -4/-6dB which should allow efficient backup dialling under all line conditions. The TONE/PAUSE ratio is 90ms/90ms. The preemphasis between low group and high group frequencies is t.m. 2.6dB. Toner ringer melody The 3 basic melody frequencies are: F 1=880Hz F 2=1067Hz F 3=1333Hz FLASH timing CPU can control the DPn pin and the MASK-mode of AS2540 via serial interface. The repetition rate is set to 4 which means that the sequence of F1, F2, F3, F1, F2, F3 is repeated 4 times within a second. Tone Ringer Ring frequency discrimination The ring frequency discrimination assures that only signals with a frequency between 13Hz and 70Hz are regarded as valid ring signals. When a valid ring signal is present for 102ms continuously, the ring melody generator is activated and remains active as long as a valid ring signal is present. Once the ring melody generator has started, the ring signal is continuously monitored and the ring melody generator is instantly turned off according to the momentary presence of a valid or invalid ring signal until next off-hook. Keyboard connections PIN MODE PIN C1 PIN C2 PIN C3 R1 R2 1 4 7 * c1 2 5 8 0 C2 3 6 9 # C3 PIN R1 PIN R2 Double contacts under keys 0-9*#: One contact is connected to AS2540, the other one to CPU. Revision 3.1 Page 9 of 18 D ata Sheet AS2540 austria micro systems Timing diagrams (unscaled) Dialling - MF mode Revision 3.1 Page 10 of 18 D ata Sheet AS2540 austria micro systems Electrical characteristics Electrical characteristics are measured with the Test Circuit application. Typical mean values will not be tested. Absolute maximum ratings Positive Supply Voltage Input Current Input Voltage (LS) Input Voltage (LI, CS) Input Voltage (STB, RI) Digital Input Voltage Electrostatic Discharge (HBM 1.5k Ω -100pF) Storage Temperature -0.3V