ADC chip control register definitions

[Ludis Langens]

Here's some information about the analog to digital chips used in
various C3 ECMs.

Texas Instruments TL530 & TL531
  40 pin DIP
  9 analog inputs
  6 dual purpose analog or digital inputs
  3 digital inputs
  3 bidirectional digital inputs/outputs
  interrupt (conversion complete) output
  68xx bus compatible

Texas Instruments TL532 & TL533
  28 pin DIP
  5 analog inputs
  6 dual purpose analog or digital inputs
  68xx bus compatible

The TL532/533 is used in popular ECM like the 1227747 and 1226870.  I
suspect that the TL530/531 is used in the very oldest ECMs - the ones in
steel (not aluminum) cases.  A few ECMs ('7747 included) contain code to
manipulate the I/O pin direction and values, even though they use the
TL532/533 which don't have these pins.  This must be an artifact of that
subroutine being used in TL530/531 equipped ECMs.

(msb)                                     (lsb)
15 14 13 12 11 10  9  8  7  6  5  4  3  2  1  0

Conversion result register (read @ offset 0):
0                                                Conversion not done
1                                                Conversion complete
   0  0  0  0  0  0  0                           Always zero
                        ?  ?  ?  ?  ?  ?  ?  ?   8 bit conversion value

Control register TL530/531 (write @ offset 2):
x                                                Don't care
   0                                             Disable interrupt
   1                                             Enable interrupt
      x  x  x  x  x                              Don't care
                     0                           Don't start conversion
                     1                           Start analog conversion
                        0                        I/O pins are inputs
                        1                        I/O pins are outputs
                           ?  ?  ?               I/O outputs
                                    ?  ?  ?  ?   Channel (0, 2-15)

Control register TL532/533 (write @ offset 2):
x  x  x  x  x  x  x                              Don't care
                     0                           Don't start conversion
                     1                           Start analog conversion
                        x  x  x  x               Don't care
                                    ?  ?  ?  ?   Channel (0, 2-5, 10-15)

Status register TL530/531 (read @ offset 2):
?  ?  ?  ?  ?  ?                                 Analog/digital inputs
                  ?  ?  ?  ?                     Analog channel select
                              ?  ?  ?            Digital inputs
                                       ?  ?  ?   I/O inputs

Status register TL532/533 (read @ offset 2):
?  ?  ?  ?  ?  ?                                 Analog/digital inputs
                  ?  ?  ?  ?                     Analog channel select
                              0  0  0  0  0  0   Always zero

-- 
Ludis Langens                               ludis (at) cruzers (dot) com
Mac, Fiero, & engine controller goodies:  http://www.cruzers.com/~ludis/