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CML Microcircuits CMX866 Manual

Modem with at commands
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CML Microcircuits
COMMUNICATION SEMICONDUCTORS
D/866/5 May 2008
Features
• V.22 bis, V.22 and Bell 212A QAM/DPSK
• V.23, Bell 202, V.21 and Bell 103 FSK
• Integral AT Command Set with 'Fast Connect'
• V.23 and Bell 202 'Fast Turnaround'
• Support for Type 1 Caller Line Identification
• DTMF/Programmable Tones: Transmit and Receive
• 'Zero-Power' and Powersave Standby Modes
• Low Power Operation
1.1

Brief Description

The CMX866 is a multi-standard modem for use in telephone based information and telemetry systems.
Control of the device is via AT commands over a simple 9600b/s serial interface, compatible with most
types of host µController. An RS232 compatible interface can be created by the addition of a Level
Converter. The data transmitted and received by the modem is also transferred over the same serial
interface. The on-chip µController interprets these AT commands and controls an internal DSP, which
provides the modem and anciliary functions such as Ring Detection, Call Progress Detection, Hook
Switch control and DTMF autodialling.
command set.
Hardware support is provided for V.23 and Bell 202 Fast Turnaround and for rapid return to AT Command
mode. A Fast Connect mode has been implemented to reduce modem connection time. Flexible line
driver and receive hybrid circuits are integrated on chip, requiring only passive external components to
build a 2 or 4-wire line interface. Complete examples of 2-wire line interfaces to an external host µC and
to an RS232 interface, including the additional components required for Type 1 CLI, are provided.
The device features a Hook Switch relay drive output and a Ring Detector circuit that remain operational
when the CMX866 is in 'Zero-Power' or Powersave mode, providing an interrupt which can be used to
wake up an external host µC, as well as the CMX866, when line voltage reversal or ringing is detected.
The device is also able to detect off-hook parallel phones by monitoring voice activity on the line.
The CMX866 takes 5mA (typ.) from a single 2.7–5.5V supply and comes in 28-pin SSOP/SOIC packages.
© 2008 CML Microsystems Plc
with AT Commands
Applications
• Telephone Telemetry Systems
• Remote Utility Meter Reading
• Security Systems
• Industrial Control Systems
• Electronic Cash Terminals / ATMs
• Pay-Phones
• Cable TV Set-Top Boxes
• EPOS Terminals
User-specific DSP functions are also available via the AT
CMX866
V.22 bis Modem
Provisional Issue

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Summary of Contents for CML Microcircuits CMX866

  • Page 1: Brief Description

    CMX866 is in 'Zero-Power' or Powersave mode, providing an interrupt which can be used to wake up an external host µC, as well as the CMX866, when line voltage reversal or ringing is detected. The device is also able to detect off-hook parallel phones by monitoring voice activity on the line.

  • Page 2: Table Of Contents

    V.22 bis Modem with AT Commands CMX866 CONTENTS Section Page Brief Description ....................1 Block Diagram .....................3 Signal List ......................4 External Components..................6 1.4.1 Ring Detector Interface .................8 1.4.2 Line Interface..................9 1.4.3 Serial Interface ..................11 1.4.4 RESETN pin ..................12 General Description..................13 1.5.1 Internal Structure .................13...

  • Page 3: Block Diagram

    V.22 bis Modem with AT Commands CMX866 Block Diagram Figure 1 Block Diagram © 2008 CML Microsystems Plc D/866/5...

  • Page 4: Signal List

    V.22 bis Modem with AT Commands CMX866 Signal List CMX866 Signal Description D1/D6 Pin No. Name Type XTALN The output of the on-chip Xtal oscillator inverter. XTAL/CLOCK The input to the oscillator inverter from the Xtal circuit or external clock source.
  • Page 5 Level Converter. This pin sends data to the external host µC which was received over the phone line. An auxiliary pin to force the CMX866 into Command Mode from Data Mode and remain off-hook. The ATO command will return the CMX866 to Data Mode.

  • Page 6: External Components

    CMX866 area, as shown in Figure 2b, with provision to make a link between them close to the CMX866. To provide a low impedance connection to ground, the decoupling capacitors (C3 – C7) must be mounted as close to the CMX866 as possible and connected directly to their respective ground plane.
  • Page 7 V.22 bis Modem with AT Commands CMX866 Figure 2b Recommended Power Supply Connections and De-coupling ANALOGUE DIGITAL C3, C6 100nF 100nF 10uF 10uF 100nH 100nH (optional, see note) (optional, see note) Note: The inductors L1 and L2 and the electrolytic capacitor C7 can be omitted without significantly degrading the system performance.

  • Page 8: Ring Detector Interface

    The signal at point X is further attenuated by the potential divider formed by R22 and R23 before being applied to the CMX866 RD input. If the amplitude of the signal appearing at RD is greater than the input threshold (Vthi) of Schmitt trigger 'A' then the N transistor connected to RT will be turned on, pulling the voltage at RT to DV by discharging the external capacitor C22.

  • Page 9: Line Interface

    V.22 bis Modem with AT Commands CMX866 If the time constant of R24 and C22 is large enough then the voltage on RT will remain below the threshold of the 'B' Schmitt trigger for the duration of a ring cycle. The time for the voltage on RT to...
  • Page 10 Rx Gain Control gain setting in the DSP Rx Mode Register (as indicated by the value held in the S26 register). The signal level into the CMX866 is affected by the line coupling transformer loss and the values of R11 and R12 of Figure 4a.

  • Page 11: Serial Interface

    RTSN is inactive high, CTSN follows RTSN and becomes inactive high, thus there is no data flow from the host µC to the CMX866, but data flow from the CMX866 to the host µC is allowed and will take place if data is received from the phone line.

  • Page 12: Resetn Pin

    The &Dn command configures these options, see section 1.5.4.4 for more details. If the RTSN pin is taken high at any time whilst the CMX866 is in Data Transfer mode, a timeout is started whose value is set in the S28 register (0 = timeout disabled). On completion of the timeout, the CMX866 will return to Command mode and take CTSN high.

  • Page 13: General Description

    10µs. If the TXD pin is tied to the DTRN pin (to implement a reduced RS232 interface) any activity on the TXD pin will also take the CMX866 into an operational state. In this case, however, data may be corrupted until the CMX866 is fully operational.

  • Page 14: Operating States And Data Flow

    V.22 bis Modem with AT Commands CMX866 1.5.2 Operating States and Data Flow The following diagram shows the flow of data in the CMX866: Figure 5a CMX866 Data Flow Diagram © 2008 CML Microsystems Plc D/866/5...
  • Page 15 V.22 bis Modem with AT Commands CMX866 The following state transition chart shows the various modes of operation for the CMX866: Figure 5b CMX866 State Transition Chart © 2008 CML Microsystems Plc D/866/5...

  • Page 16: Functional Description

    1.5.3 Functional Description The CMX866 is a multi-functional integrated modem chip which requires simple telephone line and RS232 interfaces to implement a complete, low-power modem that can be controlled by widely used AT commands. A list of the main features of this product is given below:...

  • Page 17: At Command And Register Set

    S-Register "n" Write - Write to specified S Register n =0,1 Return result codes as numbers (n=0) or words (n=1) n = 0..3 Calling and Response Characteristics Restore factory profile for CMX866 &Cn n = 0,1 DCD always on (n=0) or DCD follows carrier (n=1) &Dn n= 0..2...
  • Page 18 V.22 bis Modem with AT Commands CMX866 Parameters Function Default S Registers 5…255 DTMF tone duration and interdigit pause duration in units of 10ms 100ms 0…255 Escape code guard time in units of 50ms Reserved 0…255 General Options 0…255 Loopback carrier off time in units of 10ms 80ms 0…255...

  • Page 19: General Description Of At Commands

    ATS0=<CR> is equivalent to ATS0=0<CR>. Receipt of a back space will cause the CMX866 to send a "back space, space, back space" sequence of characters to the external host µC, to allow any terminal which may be connected to the latter to clear its screen of the last character.

  • Page 20: At Commands In Detail

    The escape sequence ‘+++’ (with Guard Time = 1s [see S12 register] before and after the sequence) will cause the CMX866 to enter Command mode from Data Transfer mode and to return an ‘OK’ response. 1.5.4.3 AT Commands in Detail...
  • Page 21 Modifier Usage n=0 When originating or answering, the CMX866 negotiates only at the specified communications standard. n=1 When originating or answering, the CMX866 falls back from V.22bis to V.22, as required (default). Change to Data Transfer Mode Used during on-line AT Command mode, this command changes the CMX866 operation to Data Transfer mode, without initiating any retrain sequence.
  • Page 22 Tx/Rx line speed, otherwise it returns a NO CARRIER result code. n=1 The CMX866 waits for a dial tone before dialling but will ignore busy tone. If a dial tone is not detected within the time in register S6, a NO DIAL TONE result code is returned.

  • Page 23: Extended At Commands

    When an on to off transition of DTR occurs (DTRN pin goes from low to high), the CMX866 goes into Command mode (if it was in Data Transfer mode), after a fixed delay of 100ms, during which time the transition is qualified.
  • Page 24 Disable remote requests for a local digital loopback connection. n=6 Request a remote digital loopback connection. Note that if the CMX866 is in Data Transfer mode, an escape sequence must be issued (+++) to return the CMX866 to Command mode before this loopback connection command can be given.
  • Page 25 'Zero-Power' state. n=1 Powersave state. The 'Zero-Power' state stops the crystal oscillator and removes power from the pin, for minimum power consumption. It takes about 30ms for the CMX866 to BIAS become fully operational from the 'Zero-Power' state. However, the crystal oscillator only takes about 1.4ms to become stable, so commands which do not...

  • Page 26: S-Registers

    If Blind Dialling is disabled, sets the length of time to wait for a dial tone after the CMX866 goes off-hook. If a dial tone is not received in this time, an 'ERROR' result code is returned.
  • Page 27 1 Originate (ATD) 0-255 10ms Loopback Carrier Off Time - To terminate a loopback test at a remote modem, the CMX866 turns off the carrier sent to that modem for the time specified in this register. 0-255 10ms Drop Time for Loopback - If a loopback test is being...
  • Page 28 V.22 bis Modem with AT Commands CMX866 S-Register Range Units Description Default 0-255 Reserved – Reserved for test functions 0-255 Reserved 0-255 Loopback and Power States - controls the operation of remote loopback and operational states: Bit 4 - Remote loopback, 0 Disabled, 1 Enabled (See &Tn command)
  • Page 29 V.22 bis Modem with AT Commands CMX866 S-Register Range Units Description Default 0-255 Tx Gain, Tx data format on phone line: Bit 2-0 - Tx Gain, 000 (-10.5dB) through to 111 (0dB) in 1.5dB steps Bit 5-3 - Tx Data/Stop bits:...

  • Page 30: Result Codes

    Command mode from Data Transfer mode. (0 = timeout disabled). 0-255 10ms Timed Break Recall Period - Sets the length of time that the CMX866 breaks the line before reconnecting it and continuing to dial the directory number. 1.5.4.6 Result Codes Numeric Response (Decimal) Word Response...
  • Page 31 XTAL frequency accuracy. Underspeed transmission is automatically handled by the CMX866 in Start-Stop mode as it inserts extra Stop bit(s) if it has to wait for new data to be loaded into the DSP Tx Data Register.

  • Page 32: Fsk And Qam/Dpsk Modulators

    V.22 bis Modem with AT Commands CMX866 1 + x -14 + x -17 1.5.6 FSK and QAM/DPSK Modulators Serial data from the USART is fed via the optional scrambler to the FSK modulator if V.21, V.23, Bell 103 or Bell 202 mode has been selected or to the QAM/DPSK modulator for V.22, V.22 bis and Bell 212A modes.

  • Page 33: Tx Filter And Equaliser

    V.22 bis Modem with AT Commands CMX866 For V.22 bis 2400bps QAM the transmit data stream is divided into groups of 4 consecutive data bits. The first two bits of each group are encoded as a phase quadrant change and the last two...

  • Page 34: Rx Dtmf/Tones Detectors

    10 of the DSP Status Register to 1 when the signal level exceeds the measurement threshold. This is handled automatically by the on-chip µController. When the CMX866 is on-hook, the Call Progress detector can be enabled so that it will detect voice activity arising from a parallel phone connection which is off-hook.

  • Page 35: Rx Modem Filterering And Demodulation

    1.5.11 Rx Modem Filterering and Demodulation When the receive part of the CMX866 is operating as a modem, the received signal is fed to a bandpass filter to attenuate unwanted signals and to provide fixed compromise line equalisation for 1200 and 2400 bps FSK, DPSK and QAM modes.

  • Page 36: Rx Modem Pattern Detectors And Descrambler

    This estimate is placed in bits 2-0 of the DSP Status Register. However, the estimate is not required for CMX866 operation and so is ignored by the on-chip µController. 1.5.12 Rx Modem Pattern Detectors and Descrambler See Figure 9a.
  • Page 37 V.22 bis Modem with AT Commands CMX866 Figure 9a Rx Modem Data Paths Whenever a new character is copied into the DSP Rx Data Register, the Rx Data Ready flag bit of the DSP Status Register is set to 1 to prompt the on-chip µController to read the new data and, in Start-Stop mode, the Even Rx Parity flag bit of the DSP Status Register is updated.

  • Page 38: Application Notes

    Hardware Interface The CMX866 can be interfaced to an external host µC, as shown in Figure 11, or to an RS232 computer port (via a level shifter IC, to generate ±6V), as shown in Figure 12. These are complete phone line interface circuits for operation at V = 5.0V.
  • Page 39 V.22 bis Modem with AT Commands CMX866 Figure 11 Host µC Example (FCC68) © 2008 CML Microsystems Plc D/866/5...
  • Page 40 V.22 bis Modem with AT Commands CMX866 Figure 12 RS232 Level Converter Example (CTR21) © 2008 CML Microsystems Plc D/866/5...
  • Page 41 V.22 bis Modem with AT Commands CMX866 Figures 11 and 12 - Component List: Reference Value Tolerance Supplier Comment C1, C2 22pF ±20% Generic C3, C4, C6 100nF ±20% Generic C5, C7 10µF ±20% Generic 100nF ±20% Generic user selectable...
  • Page 42 V.22 bis Modem with AT Commands CMX866 Reference Value Tolerance Supplier Comment R11 (FCC) 62kΩ ±1% Generic optimum value = 64k9Ω R11 (CTR21) 56kΩ ±1% Generic optimum value = 57k6Ω 100kΩ ±1% Generic 390Ω ±1% Generic optimum value = 392Ω...

  • Page 43: Calling Modem At Commands

    V.22 bis Modem with AT Commands CMX866 1.6.2 Calling Modem AT Commands General Commands for Initialisation • wake-up CMX866 from 'Zero-Power' state (pull DTRN pin low) • restore factory defaults • set Tx gain and data format ATS25=x • set communications standard...

  • Page 44: Rs232 Transaction Sequence

    V.22 bis Modem with AT Commands CMX866 1.6.4 RS232 Transaction Sequence A typical RS232 transaction sequence is shown in Figure 13 below: Figure 13 RS232 Transaction Sequence © 2008 CML Microsystems Plc D/866/5...

  • Page 45: Performance Specification

    V.22 bis Modem with AT Commands CMX866 Performance Specification 1.7.1 Electrical Performance 1.7.1.1 Absolute Maximum Ratings Exceeding these maximum ratings can result in damage to the device. Min. Max. Units Supply (V -0.3 Voltage on any pin to V -0.3 + 0.3...

  • Page 46: Operating Characteristics

    V.22 bis Modem with AT Commands CMX866 1.7.1.3 Operating Characteristics For the following conditions unless otherwise specified: = 2.7V to 5.5V at Tamb = -40 to +85°C, Xtal Frequency = 11.0592MHz ± 0.01% (100ppm) 0dBm corresponds to 775mVrms. DC Parameters Notes Min.
  • Page 47 V.22 bis Modem with AT Commands CMX866 Transmit QAM and DPSK Modes Notes Min. Typ. Max. Units (V.22, Bell 212A, V.22 bis) Carrier frequency, high band 2400 Carrier frequency, low band 1200 Baud rate Baud Bit rate (V.22, Bell 212A) 1200 Bit rate (V.22 bis)
  • Page 48 V.22 bis Modem with AT Commands CMX866 Receive QAM and DPSK Modes Notes Min. Typ. Max. Units (V.22, Bell 212A, V.22 bis) Carrier frequency (high band) 2392 2400 2408 Carrier frequency (low band) 1192 1200 1208 Baud rate Baud Bit rate (V.22, Bell 212A) 1200 Bit rate (V.22 bis)
  • Page 49 V.22 bis Modem with AT Commands CMX866 Rx Modem S1 Pattern Detector Notes Min. Typ. Max. Units (DPSK and QAM modes) Will detect S1 pattern lasting for 90.0 Will not detect S1 pattern lasting for 72.0 Hold time (minimum detector ‘On’ time)
  • Page 50 Pause length ignored 15.0 Notes: 1. At 25°C, not including any current drawn from the CMX866 pins by external circuitry other than X1, C1 and C2. 2. All logic inputs at V except for RT, DTRN and RTSN inputs which are at DV 3.
  • Page 51 V.22 bis Modem with AT Commands CMX866 Vthi Vtlo Figure 14 Typical Schmitt Trigger Input Voltage Thresholds vs. V Bell 202 1000 10000 100000 Figure 15 Maximum Out of Band Tx Line Energy Limits (see note 8) © 2008 CML Microsystems Plc...

  • Page 52: Packaging

    V.22 bis Modem with AT Commands CMX866 1.7.2 Packaging Figure 16a 28-pin SOIC (D1) Mechanical Outline: Order as part no. CMX866D1 Figure 16b 28-pin SSOP (D6) Mechanical Outline: Order as part no. CMX866D6 © 2008 CML Microsystems Plc D/866/5...
  • Page 53 V.22 bis Modem with AT Commands CMX866 Handling precautions: This product includes input protection, however, precautions should be taken to prevent device damage from electro-static discharge. CML does not assume any responsibility for the use of any circuitry described. No IPR or circuit patent licences are implied.

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