MT9092AP 查看數據表（PDF） - Mitel Networks

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MT9092AP

ISO2-CMOS ST-BUS™ FAMILY Digital Telephone with HDLC (HPhone-II)

Mitel Networks 

MT9092

PS2 PS1 PS0 Micro-program

1

0

0 handsfree switching program

1

0

1

1

1

1

1

0 Last three selections reserved

1

Note:

For the DSP to function it must be selected to

operate, in conjunction with the Filter/Codec, in

one of the B-Channels. Therefore, one of the B-

Channel enable bits must be set (see Timing

Control, address 15h : bits CH2EN and CH3EN).

Power Up reset Program

A hardware power-up reset (pin 6, PWRST) will

initialize the DSP hardware registers to the default

values (all zeros) and will reset the DSP program

counter. The DSP will then be disabled and the PCM

streams will pass transparently through the DSP. The

RAM-based registers are not reset by the PWRST

pin but may be initialized to their default settings by

programming the DSP to execute the power up reset

program. None of the micro-programs actually

require the execution of the power up reset program

but it is useful for pre-setting the variables to a

known condition. Note that the reset program

requires one full frame (125µSec) for execution.

Gain Control Program

Gain control is performed on converted linear code

for both the receive and the transmit PCM. Receive

gain control is set via the hardware register at

address 1Dh (see bits B0 - B5) and may be changed

at any time. Gain in 1.5dB increments is available

within a range of +22.5dB to -72dB. Normal

operation usually requires no more than a +20 to -20

dB range of control. However, the handsfree

switching algorithm requires a large attenuation

depth to maintain stability in worst case

environments, hence the large (-72 dB) negative

limit. Transmit gain control is divided into two RAM

registers, one for setting the network level of transmit

speech (address 20h) and the other for setting the

transmit level of DTMF tones into the network

(address 21h). Both registers provide gain control in

1.5dB increments and are encoded in the same

manner as the receive gain control register (see

address 1Dh, bits B0 - B5). The power up reset

program sets the default values such that the receive

gain is set to -72.0 dB, the transmit audio gain is set

to 0.0dB and the transmit DTMF gain is set to -3.0

dB (equivalent to a DTMF output level of -4dBm0 into

the network).

Optional Offset Nulling

Transmit PCM may contain residual offset in the form

of a DC component. An offset of up to ±fifteen linear

bits is acceptable with no degradation of the

parameters defined in CCITT G.714. The HPhone-II

filter/CODEC guarantees no more than ±ten linear

bits of offset in the transmit PCM when the autonull

routine is not enabled. By enabling autonulling (see

AUTO in the Receive Gain Control Register, address

1Dh) offsets are reduced to within ±one bit of zero.

Autonulling circuitry was essential in the first

generations of Filter/Codecs to remove the large DC

offsets found in the linear technology. Newer

technology has made nulling circuitry optional as

offered in the HPhone-II.

DTMF and Gain Control Program

The DTMF program generates a dual cosine wave

pattern which may be routed into the receive path as

comfort tones or into the transmit path as network

signalling. In both cases, the digitally generated

signal will undergo gain adjustment as programmed

into the Receive Gain Control and the Transmit

DTMF Gain Control registers. The composite signal

output level in both directions is -4dBm0 when the

gain controls are set to 2Eh (-3.0 dB). Adjustments to

these levels may be made by altering the settings of

the gain control registers. Pre-twist of 2.0dB is

incorporated into the composite signal. The

frequency of the low group tone is programmed by

writing an 8-bit coefficient into Tone Coefficient

Register 1 (address 23h), while the high group tone

frequency uses the 8-bit coefficient programmed into

Tone Coefficient Register 2 (address 24h). Both

coefficients are determined by the following

equation:

COEFF = 0.128 x Frequency (in Hz)

where COEFF is a rounded off 8 bit binary integer

A single frequency tone may be generated instead of

a dual tone by programming the coefficient at

address 23h to a value of zero. In this case the

frequency of the single output tone is governed by

the coefficient stored at address 24h.

7-9

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