Serial connection
george miyagi
Posts: 48
I see in the SuperCarrier schematic that the serial pins, 6, 2, and 7 are all connected to BS2 pin 1. what is the reason for connecting the 6 and 7 pin?
www.parallax.com/dl/docs/prod/schem/supercarrierbd.pdf
tx
www.parallax.com/dl/docs/prod/schem/supercarrierbd.pdf
tx
Comments
I think if you look more closely, pins 6 and 7 are tied together and form the "loopback" facility. Pins 2, 6 and 7 are NOT tied together at the serial connector. Only serial pin 2 goes to the Stamp pin 1 (Rx to Sin).
Regards,
Bruce Bates
what does the loopback do?
Before the Stamp Editor attemps to access the PBASIC Stamp Module itself, it performs a number of tests in an attempt to make sure there is something at the end of the serial connection, other than free air, before it begins to utilize it.
One of these tests is the "loopback test" used by many intelligent programs to "prove" that something other than free air exists at the end of the serial connection. All it proves is that continuity exists between pins 6 and 7 (arbitrarily chosen, often unused) - no more, and no less. It is one indication that SOMETHING is ... out there. At the end of this test there is no guarantee that a PBASIC Stamp Module is out there, just something that will pass a LOOPBACK test.
The next test it performs is to see if a character or set of characters transmitted to the entity attached can be received back (reflected) by the Stamp Editor. This is "proof" that not only is there something out there, but it's at least a reflector of transmitted data, and another indication that it may well be a Stamp Module. This is known as the ECHO test.
The last indicative test, which may or may not be performed, is the IDENTIFY facility of the Stamp Editor. This command actually queries the entity at the other end of the serial connection, and requests specific information; namely the type and version of the (proposed) Stamp Module now presumed to be at the end of the serial connection. If the preceeding checks are affirmative, and this IDENTIFY check is successful, then there is little question that the entity at the other end of the serial connection is indeed a Parallax BASIC Stamp.
Regards,
Bruce Bates