122-32000 Parallax Inc, 122-32000 Datasheet - Page 26

• Manufacturer Part Number: 122-32000
• Description: MANUAL PROPELLER
• Manufacturer: Parallax Inc

Specifications of 122-32000

• Accessory Type: Manual
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• For Use With/related Products: Propeller Education (PE) Kit
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

I/O Pins
The Propeller has 32 I/O pins, 28 of which are entirely general purpose. Four I/O pins (28 -
31) have a special purpose at Boot Up and are available for general purpose use afterwards;
see the Boot Up Procedure section on page 18. After boot up, any I/O pins can be used by
any cogs at any time since I/O pins are one of the common resources. It is up to the
application developer to ensure that no two cogs try to use the same I/O pin for different
purposes during run-time.
Each cog has its own 32-bit I/O Direction Register and 32-bit I/O Output Register. The state
of each cog’s Direction Register is OR’d with that of the previous cogs’ Direction Registers.
Similarly, each cog’s output states is OR’d with that of the previous cogs’ output states. Note
that each cog’s output states are made up of the OR’d states of its internal I/O hardware and
that is all AND’d with its Direction Register’s states. The result is that each I/O pin’s
direction and output state is the “wired-OR” of the entire cog collective. No electrical
contention between cogs is possible, yet they can all still access the I/O pins simultaneously!
The result of this I/O pin wiring configuration can easily be described in the following simple
rules:
Table 1-4 demonstrates a few possible combinations of the collective cogs’ influence on a
particular I/O pin, P12 in this example. For simplification, these examples assume that bit 12
of each cog’s I/O hardware, other than its I/O Output Register, is cleared to zero (0).
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A. A pin is an input only if no active cog sets it to an output.
B. A pin outputs low only if all active cogs that set it to output also set it to low.
C. A pin outputs high if any active cog sets it to an output and also sets it high.