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linlog.hlp
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1991-11-26
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46 lines
Name: LINLOG.ASM
Type: Assembler Macros
Version: 1.0
Date Entered: 20-Apr-87
Last Change: 20-Apr-87
Description: Linear PCM to Companded CODEC Data Conversion Macros
These macros convert 13 bit, linear fractional data into 8 bit companded
data suitable for transmission to CODEC D/A converters used in
telecommunications applications. Four companded formats are
supported for the Motorola MC14400 CODEC series and similar devices.
Macro Name Description
---------- -----------
linsm linear to sign magnitude conversion with mu-law companding.
linmu linear to mu-law companded conversion without zero code
suppression.
lind3d4 linear to mu-law companded conversion with D3/D4 format
zero code suppression.
linal linear to a-law companded conversion with CCITT (G7.12)
format.
Input data is a 56 bit number in accumulator a. Although any 56 bit
number may be used, the 13 bit linear fraction is assumed to be in
the most significant bits of a1. Values outside this fractional range
are automatically converted to a maximum positive or negative companded
value (dynamic range limiting).
Output data is in the 8 most significant bits of a1. The 16 LSB's
of a1 are zero.
-------------------------------------------------------
| Sign | Chord Number | Step Number |
| Bit | | |
|__23__|__22_____21_____20__|__19_____18_____17_____16__|
These macros execute in 23-25 instruction cycles worst case and require
16-18 words of program memory. They do not use the DSP56001 internal
mu/a-law lookup table.