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INTERFACE WITH THE DSP56156 CORE PROCESSOR
up to 3dB below the full scale saturation values. The full scale saturation analog values
result in a maximum digital A/D output ($7FFF) when the A/D comb filter has a unity gain.
MGS1 MGS0
0
0
1
1
6.4.5.5
COCR Input Select Bit (INS) Bit 13
The input select bit is used by the DSP to select between the two inputs MIC and AUX.
When INS is cleared, MIC is selected and when INS is set, AUX input is selected.
6.4.5.6
COCR Codec Enable Bit (COE) Bit 14
The Codec Enable Bit enables the on-chip codec section. When this bit is cleared the sec-
tion is disabled and put in the power down mode. Setting the bit wakes-up and enables
the on-chip codec section.
6.4.5.7
COCR Codec Interrupt Enable Bit (COIE) Bit 15
The Codec Interrupt Enable Bit enables the on-chip codec interrupt. When this bit is
cleared the interrupt is disabled. Setting this bit enables the interrupt.
6.4.5.8
COCR Reserved Bits (Bits 4-7)
These bits are reserved. They should be written as zero by the user program and will read
as zero.
6.4.6
Codec Status Register (COSR)
The Codec Status Register COSR is an 8-bit read-only status register used by the DSP
to interrogate the status and flags of the on-chip codec. The status bits and flag bits are
described in the following paragraphs.
6.4.6.1
COSR Codec Transmit Under Run Error FLag Bit (CTUE) Bit 0
The Codec Transmit Under Run Error flag bit is set when a sample has to be transmitted
to the codec section while the DSP has not yet written to the CTX transmit register (under
run error). In this case, the previous sample written to the CTX register is re-transmitted
to the D/A section.
Hardware and software reset and STOP reset clear CTUE. CTUE is also cleared by read-
ing the COSR with CTUE set followed by writing CTX. Clearing the COE bit in the COCR
does not affect CTUE.
MOTOROLA
Table 6-5 Microphone Gain Control
Gain
Actual
0
0.5
1
1
0
2
1
7.07
DSP56156 ON-CHIP SIGMA/DELTA CODEC
Modulator
Full scale
dB
full scale
linearity
-6
2 Vp
1.414 Vp
0
1 Vp
0.707 Vp
6
500 mVp
354 mVp
17
141 mVp
100 mVp
6 - 9
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