Using the SX28 Socket on the BS Professional Development Board

awesomeduck

I'm working on some rather complex projects and breadboard space on the PDB is running out. Looking at the schematics for the PDB it appears there is an easy way to extend the I/O on the board by inserting a 74165 in the lower portion of the SX-28 socket. As long as you not using the 40 pin BS, this is an easy way to expand the inputs for infrequently read devices like the DIP switches. A similar trick could be used with the 74595 too. A neat way to pick up 8 more IO pins on the PBD without going to a BSp40 and not using up any breadboard space.

Carl Hayes

Well, I don't think you gain 8 inputs by a 74165, but you can gain 6. The reason you don't gain 8 is that you've got to use one of your existing pins to read the 74165, and another to clock it. So you gain 8 but lose 2. If you have a place to put another 75165, though, you gain 8 more with that one, for you can cascade the two 74165s onto a single output (connected to a Stamp input), and clock them both with the same clock signal. All of that applies to the 74595, of course.

This is a neat idea, very creative.

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· -- Carl, nn5i@arrl.net

Carl Hayes

Oops, I guess you actually gain 5. You've got to have another signal to the 74165 to load it, and to inhibit loading while you shift it. I've never used a 74165, and it's late, so I may have missed something.

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· -- Carl, nn5i@arrl.net

Carl Hayes

Actually you get 6. The extra one comes from using the serial input. The 74165 actually has eight parallel inputs and one serial input. You can load the whole shift register from the parallel input, then pump it from 0 to 7 times to get out the one you're after (by pulsing the clock input). That's eight inputs. But you can also pump it an eighth time, and out will come whatever's at the serial input. Neat.

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· -- Carl, nn5i@arrl.net