PAK-III Datasheet, PDF (6/14 Pages) List of Unclassifed Manufacturers – Using the PAK-III I/O Coprocessor

I/O Considerations
Each I/O pin on the Pak III can sink 25mA or source 20mA subject to a total limit of
150mA total sink and 100mA total source. Inputs consider voltages below .8V as a 0 and
voltages greater than 2.4V as a 1. Outputs will be less than .6V or greater than 4.3V (for a
1 or a 0, respectively).
Resetting
There are several ways you can reset the Pak III. It is a good idea to reset the unit before
using it, or any time that you want to make sure it is in a known state. This is especially
true when using the Stamp. Each time the Stamp resets or wakes up from sleep, the I/O
pins briefly become inputs. This can fool the Pak III into starting a data transfer. Always
reset the Pak III first.
The best way to reset the Pak III (when using only one unit) is to send a special reset
sequence over the clock and data lines. This has the advantage that it doesn't require any
extra I/O from the host. To send a reset sequence, bring the data pin to 0 and raise the
clock to a 1. While the clock remains in the 1 state, bring the data pin high. This will
indicate to the Pak III that you wish to reset. When the clock returns to a zero state, the
Pak III will reset. The reset doesn't change any register values or port pins, but it does
reset communications to a known state.
You can get the same result by bringing the enable pin low and then returning it to high
to enable the Pak III. This is useful if you are connecting more than one Pak to the same
data and clock lines. You'll need to use the enable pin then anyway, and it makes sure
that the selected Pak is always in a known state. Don't use the data line reset when using
multiple Paks on the same clock and data lines.
Finally, you can force a hardware reset by bringing the reset pin low. This might be
useful if your circuit generates a hardware reset signal based on a brown-out detector or
other master reset circuit. Normally, you'll just connect the reset pin to the +5V supply
and allow the Pak III to reset itself on power up. If you do want to drive this pin, make
sure that it is at 5V for normal operation. You can use a reset switch or other device if
you pull up the reset pin with a 10K-22K resistor. This is the only reset that will interrupt
an operation in progress.
Communications
There are several schemes you can use to communicate with the Pak III. All of them
revolve around a synchronous protocol involving a clock pin and 1 or 2 data pins. Data is
shifted most significant bit first, and samples at the rising edge of the clock. The Pak III
exposes a separate input (SIN) and output (SOUT) pins for hosts that can't easily handle
bi-directional I/O lines. However, for hosts like the Stamp or PIC, it is a simple matter to
tie these lines together since SOUT is open collector.
Therefore, the minimum number of lines you need are two. An output for the clock and
an I/O line to connect to SIN and SOUT. You'll connect the Enable/Busy pin to +5V and
use a pull up resistor to 5V on the Busy/Mode pin. This allows you to reset the device