mt9094apr1 Zarlink Semiconductor, mt9094apr1 Datasheet - Page 7

• Manufacturer Part Number: mt9094apr1
• Description: Fully Featured Digital Telephone Circuit With Embedded Dsp For Tone Generation And Hands Free Operation
• Manufacturer: Zarlink Semiconductor

Note:
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 1.5 dB
increments is available within a range of +22.5 dB to -72 dB. 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
1.5 dB 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 -4 dBm0 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 DPhone-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
DPhone-II.
0
0
0
1
1
1
1
Therefore, one of the B-Channel enable bits must be set (see Timing Control, address 15h: bits CH
For the DSP to function it must be selected to operate, in conjunction with the Filter/Codec, in one of the B-Channels.
0
1
1
0
0
1
1
1
0
1
0
1
0
1
Transmit and receive gain control program; with autonulling of the transmit PCM, if the AUTO bit is
DTMF generation plus transmit and receive gain control program (autonull available via the AUTO
Tone ringer plus transmit and receive gain control program (autonull available via the AUTO control
handsfree switching program
Last three selections reserved
set (see address 1Dh)
control bit)
bit)
Zarlink Semiconductor Inc.
MT9094
7
2
EN and CH
Data Sheet
3
EN).