MX812 Просмотр технического описания (PDF) - MX-COM Inc

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MX812

VSR CODEC WITH DRAM CONTROL

MX-COM Inc  

VSR CODEC with DRAM CONTROL

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MX812 PRELIMINARY INFORMATION

DESCRIPTION

The MX812 is a half-duplex VSR Codec, which

when connected to an audio processing microcircuit

(such as the MX816, 826 or 836), provides the storage

and recovery of speechband audio in attached Dynamic

RAM. The addition of this device will enhance the

communications system by providing cellular radios

with Answering Functions, “Message-Notepad” and

general announcement cababilities.

The MX812 will enable:

• Storage of a speech message for transmission

(replay) at a later time.

• Storage of a received speech message when the

operator is not attending.

• The storage and subsequent replay of speech.

All VSR operating functions are controlled by a

simple serial µProcessor interface which may operate

from the radio’s own µProcessor/Controller.

Input audio from the “Store” output of the audio

processor is digitized by delta modulation and stored

via the DRAM controller, in attached memory.

Audio for replay is recovered from the assigned

memory locations and after demodulation made

available for supply to the “Play” input of the audio

processor. For use with other audio systems, the input/

output audio can be connected to relevant points in

circuit.

The MX812 has no on-chip input or output audio

filtering; this capability must therefore be provided by

the host system. Sampling rates and memory capacity

are selectable to 32kb/s or 63kb/s and 1 x 4Mbit or 2 x

1Mbit respectively, which when used in conjunction

allow control of audio-quality and storage-time.

This low-power CMOS device is available 28-pin

plastic SOIC and 28-pin Cerdip packages.

Pin

Function

1 CAS: This output should be connected to the “Column Address Strobe” input pin(s) of all DRAM

devices installed.

2 WE: This output should be connected to the “Write Enable” input pin(s) of all DRAM devices installed.

3 D: Digital (speech) data into and out of the VSR Codec. This pin should be connected to the “Data

In” and “Data Out” pins (“D” and “Q”) of DRAM devices.

4 Xtal: The nominal 4.0MHz clock input to the VSR Codec. The signal applied to this device may be

derived from the attached Audio Processor on-chip Xtal Oscillator circuits (see Figures 2 and 3).

Note that the VSR Codec will be able to function and maintain correct DRAM refresh, with Xtal input

frequencies down to 2.0MHz. Compand and Local Decoder time constants will change accordingly

and minimum “C-BUS” timings (Figures 6 and 7) would have to be increased pro-rata.

5 Interrupt Request (IRQ): This Interrupt Request output from the MX812 is ‘wire-OR able’ allowing

the Interrupt Outputs of other peripherals to be commoned and connected to the Interrupt input of the

µProcessor (see the C-BUS Interface and System Applications document). This input has a low-

impedance pulldown to VSS when active, and a high-impedance when inactive.

6 Serial Clock: The C-BUS serial clock input. This clock produced by the µController, is used for

transfer timing of commands and data to and from the VSR Codec. See Timing Diagrams.

7 Command Data: The C-BUS serial (command) data input from the µController. Data is loaded to

this device in 8-bit bytes MSB (B7) first and LSB (B0) last, synchronized to the Serial Clock.

8 Chip Select (CS): The C-BUS data transfer control function. This input is provided by the

µController. Transfer sequences are initiated, completed or aborted by this signal. See Timing

Diagrams.

9 Reply Data: The C-BUS serial data output to the µController. The transmission of reply bytes is

synchronized to the Serial Clock under the control of the Chip Select input. This is a 3-state output

which is held at a high-impedance when not sending data to the µController.

10 VBIAS: The output of the internal analog circuitry bias line, held internally at VDD/2. This pin should be

decoupled to V by capacitor C (see Figure 2).

SS

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© 1997 MX•COM Inc.

www.mxcom.com Tele: 800 638-5577 910 744-5050 Fax: 910 744-5054

Doc. # 20480076.003

4800 Bethania Station Road, Winston-Salem, NC 27105-1201 USA All trademarks and service marks are held by their respective companies.

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