Deciding the nature of various connecting interfaces
01-06-2011, 07:58 AM CODE 5-112
First, decide if the interface will use one pin or two pins. A two wire interface (2 pins per chip) can operate in a bi-directional full duplex mode (send and receive at the same time or staggered). It can also be configured to function with one wire out of the two as half duplex.
One wire (1 pin per chip) functions in half duplex mode. It can either send or receive but not both at the same time. One wire interfacing has the advantage of simplicity, can be up and running in a timely fashion, and has low code overhead potentially needing only a single cog.
Standard One-Pin Uni-Directional True/Inverted Mode
Standard Two-Pin Bi-Directional True/Inverted Modes
Same-Pin (Bi-Directional) Inverted Mode
Same-Pin (Bi-Directional) True Mode
of protection resistors)
The napkin sketch shows four connection diagrams, less the protection resistors on each Propeller. Not the pull up and pull down configurations with a 4K7 resistor in bi-directional true and inverted modes. One pin bi-directional mode in inverted mode and pull down was adopted by BSS (illustration number 4). For simplicity, reliability and familiar code, illustration 4 will be adapted first unless otherwise noted.