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+FreeCalypso Venus will have the same 21-button main keypad as on TI's D-Sample
+development platform, as seen in this photograph:
+
+https://www.freecalypso.org/members/falcon/pictures/D-Sample/pic1.jpeg
+
+Each of these 21 buttons forming the main keypad underneath the LCD will be an
+E-Switch TL3301 series SMT tactile switch, mounted directly on the top side of
+FC Venus board.  The following reference designators are assigned to these 21
+tactile switches:
+
+S401 [LS]	S402 [^]	S403 [RS]
+S404 [<-]	S405 [.]	S406 [->]
+S407 [Green]	S408 [V]	S409 [Red]
+
+S410 [1]	S411 [2]	S412 [3]
+S413 [4]	S414 [5]	S415 [6]
+S416 [7]	S417 [8]	S418 [9]
+S419 [*]	S420 [0]	S421 [#]
+
+The label in square brackets indicates logical function:
+
+* [Green] and [Red] are the green call key (traditionally called SEND) and the
+  red power/hang-up key (traditionally called END).
+
+* [LS] and [RS] are the left and right "soft function" keys, above [Green] and
+  [Red] and directly below the LCD.
+
+* S402, S404, S405, S406 and S408 form the 5-way navigation button group (S405
+  is "center"); their [] labels are an ASCII art attempt to depict navigation
+  key directions.
+
+* S410 through S421 form the most traditional 12-button dial keypad.
+
+In addition to these 21 tactile switches forming the main keypad, there will be
+3 additional tactile switches of the same type corresponding to the 3 side
+buttons on D-Sample:
+
+S422	Left side button: volume up
+S423	Left side button: volume down
+S424	Right side button, function unspecified
+
+S422 and S423 will need to be placed on the left side of our LCD; S424 will need
+to be placed to the right of our LCD.
+
+S409 will be connected between PWON and GND and thus exist outside of KBC/KBR
+matrix.  Each of the remaining 23 keyswitches will short across a KBC/KBR pair.
+Calypso provides 5 KBC and 5 KBR lines, allowing for up to 25 keyswitches, thus
+enough for our 23.  The choice of which KBC/KBR crosspoint should be used for
+which button position is up to the PCB layout engineer - the source file to be
+edited is src/periph/keypad.v.