Hello all,
I have been given and old wacom tablet with ADB connection. I checked past
posts, searched on the internet and haven't found too many articles about
connecting ADB devices to the PC.
Thus I went to library, and found out how the connection was realized at old
apple computers (this concrete one is at mac portable). Which I think can be
taken as it is, and can be connected to the parallel pc port as shown
bellow:
+5V >----o--------.
| |
.-. .-.
| |10k | |470
'-' '-'
LPT: | |
10 | |
nAck <-------------------o---------o-------> ADB
| ____|
2 | | /
D0 >----------o-----------|/ NPN (2N3904)
|\
18 _\/
GND >----------. |
| |
_|_ _|_
GND GND
My question is whether is there someone with electro-engeneering background
who could verify and give me some feedback about the schematic above? Would
it be possible to wire ADB to the port with less parts? Has anyone tried
something similar before?
Another thing is, I suppose, that by adding 2 zener diodes it should be
possible get ADB out of serial port, since this bus seems electrically quite
similar to I2C.
Also, are there some more developers reading this list who has ADB tablet
somewhere in the corner of the room and thinking about making it working? If
we will find a way how to wire it to the PC, I believe that sources listed
at the end contains enough information for implementing an driver.
Here are some more tech details:
ADB is bi-directional data bus with variable-pulse-width having
open collector signal pulled up to +5V throught 470ohm resistor.
these are electrical characteristic of ADB for Mac SE:
_____________________|__ Min___|___Max_________
Low input voltage | -0.2V | 0.8V
High input voltage | 2.4V | 5.0V
Low output voltage | --- | 0.45V (12mA)
High output voltage | 2.4V | ---
-----------------------------------------------
Device output current when off: -20microA (0.4V)
Device input capacitance: 150pF
Where all devices must not draw more than 500mA total from +5V supplied
Cables should not be longer than 5m and capacitance should not exceed
100pF/m
sources:
Apple Macintosh Family Hardware Reference, AW, 1988. (0-201-19255-1)
Inside Macintosh - Volume V., Apple/AW, 1986.
Guide to Macintosh Family Hardware, Apple Computer Inc./AW, 1990.
http://en.wikipedia.org/wiki/Apple_Desktop_Bus
http://developer.apple.com/documentation/Hardware/Developer_Notes/\
Macintosh_CPUs-G3/PowerMacintosh_G3/PowerMacG3.2b.html
http://developer.apple.com/documentation/mac/Devices/Devices-205.html
Regards,
Adam Kral
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