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PDF CMX867 Data sheet ( Hoja de datos )
| Número de pieza | CMX867 | |
| Descripción | Low Power V.22 Modem | |
| Fabricantes | CML Microcircuits | |
| Logotipo |  |
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D/867/2 November 2001
Features
• V.22, Bell 212A 1200/1200 or 600/600 bps DPSK
• V.23 1200/75, 1200/1200, 75, 1200 bps FSK
• Bell 202 1200/150, 1200/1200, 150, 1200 bps FSK
• V.21 or Bell 103 300/300 bps FSK
• DTMF/Tones Transmit and Receive
• ‘Powersave’ Standby Mode
• Software and Hardware Compatible with CMX868
CMX867
Low Power
V.22 Modem
Provisional Information
Applications
• Telephone Telemetry Systems
• Remote Utility Meter Reading
• Security Systems
• Industrial Control Systems
• Electronic Cash Terminals
• Pay-Phones
• Cable TV Set-Top Boxes
1.1 Brief Description
The CMX867 is a multi-standard modem for use in telephone based information and telemetry systems.
Control of the device is via a simple high speed serial bus, compatible with most types of µC serial
interface. The data transmitted and received by the modem is also transferred over the same serial bus.
On-chip programmable Tx and Rx USARTs meeting the requirements of V.14 are provided for use with
asynchronous data and allow unformatted synchronous data to be received or transmitted as 8-bit words.
It can transmit and detect standard DTMF and modem calling and answer signals or user-specific
programmed single or dual tone signals. A general purpose Call Progress signal detector is also included.
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.
The device also features a Hook Switch Relay Drive output and a Ring Detector circuit which continues
to function when the device is in the Powersave mode, providing an interrupt which can be used to wake
up the host µController when line voltage reversal or ringing is detected.
The CMX867 operates from a single 2.7 to 5.5V supply over a temperature range of -40°C to +85°C and
is available in 24-pin TSSOP, SOIC and DIP packages.
© 2001 Consumer Microcircuits Limited
1 page  
Low Power V.22 Modem
Notes:
I/P
O/P
BI
T/S
NC
=
=
=
=
=
Input
Output
Bidirectional
3-state Output
No Connection
1.4 External Components
CMX867
R1 100kΩ
X1 11.0592MHz
or 12.288MHz
C1, C2
C3, C4
C5
22pF
100nF
10uF
Resistors ±5%, capacitors ±20% unless otherwise stated.
Figure 2 Recommended External Components for Typical Application
This device is capable of detecting and decoding small amplitude signals. To achieve this VDD and
VBIAS should be decoupled and the receive path protected from extraneous in-band signals. It is
recommended that the printed circuit board is laid out with a VSS ground plane in the CMX867 area to
provide a low impedance connection between the VSS pins and the VDD and VBIAS decoupling capacitors.
The VSS connections to the Xtal oscillator capacitors C1 and C2 should also be low impedance and
preferably be part of the VSS ground plane to ensure reliable start up of the oscillator.
For best results, an Xtal oscillator design should drive the clock inverter input with signal levels of at least
40% of VDD peak-to-peak. Tuning-fork Xtals generally cannot meet this requirement. To obtain Xtal
oscillator design assistance, please consult your Xtal manufacturer.
© 2001 Consumer Microcircuits Limited
5
D/867/2
5 Page 
Low Power V.22 Modem
CMX867
In all modes the transmitted bit and baud rates are the nominal rates for the selected modem type, with
an accuracy determined by the XTAL frequency accuracy, however for DPSK modes V.14 requires that
Start-Stop characters can be transmitted at up to 1% overspeed (basic signalling rate range) or 2.3%
overspeed (extended signalling rate range) by deleting a Stop bit from no more than one out of every 8
(basic range) or 4 (extended range) consecutive transmitted characters.
To accommodate the V.14 requirement the Tx Data Register has been given two C-BUS addresses, $E3
and $E4. Data should normally be written to $E3.
In DPSK Start-Stop modes if data is written to $E4 then the programmed number of Stop bits will be
reduced by one for that character. In this way the µC can delete transmitted Stop bits as needed.
In FSK Start-Stop modes, data written to $E4 will be transmitted with a 12.5% reduction in the length of
the Stop bit at the end of that character.
In all Synchronous Data modes data written to $E4 will be treated as though it had been written to $E3.
The underspeed transmission requirement of V.14 is automatically met by the CMX867 as in Start-Stop
mode it automatically inserts extra Stop bit(s) if it has to wait for new data to be loaded into the C-BUS
Tx Data Register.
The optional V.22 compatible data scrambler can be programmed to invert the next input bit in the event
of 64 consecutive ones appearing at its input. It uses the generating polynomial:
1 + x-14 + x-17
1.5.2 FSK and 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 DPSK modulator for V.22 and Bell 212A modes.
The FSK modulator generates one of two frequencies according to the transmit mode and the value of
current transmit data bit.
The DPSK modulator generates a carrier of 1200Hz (Low Band, Calling modem) or 2400Hz (High Band,
Answering modem) which is modulated at 600 symbols/sec as described below:
600bps V.22 signals are transmitted as a +90° carrier phase change for a ‘0’ bit, +270° for ‘1’.
For V.22 and Bell 212A 1200bps DPSK the transmit data stream is divided into groups of two
consecutive bits (dibits) which are encoded as a carrier phase change:
Dibit
(left-hand bit is the
first of the pair)
00
01
11
10
Phase change
+90°
0°
+270°
+180°
© 2001 Consumer Microcircuits Limited
11
D/867/2
11 Page | ||
| Páginas | Total 30 Páginas | |
| PDF Descargar | [ Datasheet CMX867.PDF ] | |
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