THERM_C

This logic has the following hierarchy:

  THERM.ABL
  |
  +- DISP3.abl
  |	LED_AC.alb
  |	HEX27SEG.alb
  +- HEX2BCD.abl
  |	DIV8.abl
  |	  MULT8.abl
  |	    SHIFT16
  |           SHIFT8
  |         SHIFT8
  +- CLOCKB
  +- IIC

What the logic Does:
====================
This logic is in essence a LM75 controller.  LM75 is a thermal sensor which 
interfaces to a microprocessor via inter-intergrated chip bus (IIC).  This
sensor provides a real time temperature which is updated once a second.

This logic, completes a digital thermometer based around the LM75.  The 
controller samples the LM75, formats the raw data and diplays the temperature
data into a multiplexed 3 digit display.  Temperature displayed can be in 
celcius or fahrenheit.  

Design Features:
================
o Supports Celcius and Fahrenheit temperature modes
o Hex to BCD converter
o Uses any LM75 compatible thermal sensors (TCN75, etc)
o Multipliexed 3 digit 7-segment LED display driver
o Bidirectional IIC serial port
o Fixed point unsigned divider of the form 16/8
o Supports upto 2 LM75 devices for dual temperature monitoring

Design Environment:
===================
The logic was written using ABEL v5.0 


Design Notes:
=============

Fahrenheit/Celcius
------------------
The fahrenheit conversion uses fixed point integer math. Recall that the deg C to
fahrenheit relationship is defined as:

	F = 9/5 * C + 32

This equation is implemented as:

	F =(230 * C)>>7 + 32

That is, the deg C data is multiplied by a fixed constant of 230, then divided by
128 (right shift by 7) and a constant of 32 added to it.


Fixed unsigned Divider
----------------------
The fixed unsigned divider is implemented as a succesive approximation logic.

Fixed 8bit unsigned Multiplier
-------------------------
The fixed unsigned multiplier is implemented using the pen-paper algorithm.
That is, shift add.

Hex to BCD conversion
---------------------
Hex to binary coded decimal conversion is implemented using the pen-paper 
algorithm.  That is, the Hex data is successively divided by a constant of 10. Tje
Result is then divided by 10 again.