from pins_arduino.h - Pin definitions, tables and functions for Arduino
  Part of Arduino - http://www.arduino.cc/ Copyright (c) 2007 David A. Mellis */
tersified by DGerman@Real-World-Systems.com for easier reading (c)2012 Dennis G German
Not expected to be compilable!  Not all syntax is exact nor 8/16 bit explicit

NUM_DIGITAL_PINS            20
NUM_ANALOG_INPUTS            6    ( on 28 in packages!)

// assigning index numbers to pins permitts accessing these tables in flash
analogInputToDigitalPin(p)  ((p < 6) ? (p) + 14 : -1)  AD0 aka D0+14

digitalPinHasPWM(p)  1 for p=3, 5, 6, 9, 10, 11     ATmega8 doesn't do 3, 5, 6

const static uint8_t                          ++++ why are these static constants instead of compiler variables ie define SS 10
SS  = 10; MOSI = 11; MISO = 12; SCK  = 13;    ++++        this means SDA=1 cannot be SBI SDA rather LD r,SDA; SL r<SDA ; out r    ?????(_) 
SDA = 18; SCL = 19;                           
                                            

LED_BUILTIN = 13; // on Duemilanova
// LED_BUILTIN =  9;  // on ethernet
A0 = 14; A1 = 15; A2 = 16; A3 = 17; A4 = 18; A5 = 19; A6 = 20; A7 = 21;

EECR   1F               !(General Purpose) I/O Registers               Atmega Section 30. Register Summary 
GPIOR0 1E               IN,OUT 00:1F  or   LD,ST (address+ 0x20 )          (addreses not shown are reserved)
EIMSK  1D               bit-accessible using  
EIFR   1C               SBI A,v (set) , CBI(clear) v=0:7 
PCIFR  1B               SBIS(SkipifSet), and SBIC(SkipIfClear)  
TIFR2,1,0  17,16,15
PORTD,C,B  0B,08,05
DDRD,C,B   0A,07,04
PIND,C,B   09,06,03


//            PinChangeInterruptControlRegister and Mask    Atmega Section 12.2 (not PC15 not available)
digitalPinToPCICR(p)     1 for  <= 0 p < 22
digitalPinToPCICRbit(p) (p) <= 7) ? 2 : (((p) <= 13) ? 0 : 1))
                         01 for 0:7, 02 for 8:14, 04 for 15:22

digitalPinToPCMSK(p)    (((p) <= 7) ? (&PCMSK2) : (((p) <= 13) ? (&PCMSK0) : (((p) <= 21) ? &PCMSK1 :  *0 )))
            11111110 1111101 11111011 11110111 11101111 11011111 101111111 011111111  PCMSK0       
            11111110 1111101 11111011 11110111 11101111 11011111 101111111 011111111               PCMSK1       
            11111110 1111101 11111011 11110111 11101111 11011111 101111111 011111111                          PCMSK2
digitalPinToPCMSKbit(p) (((p) <= 7) ? (p) : (((p) <= 13) ? ((p) - 8) : ((p) - 14)))                
            00000001 0000010 00000100 00001000 00010000 00100000 010000000 100000000  PCMSK0
            00000001 0000010 00000100 00001000 00010000 00100000 010000000 100000000               PCMSK1
            00000001 0000010 00000100 00001000 00010000 00100000 010000000 100000000                           PCMSK2
                                                                                     7 ...... 0  14 .....8  23 .......16  
// digital pins are also used for the analog output (software PWM PulseWidthModulation).  

// ATMEL ATMEGA8 & 168 / ARDUINO
//
//                  +-\/-+
//            PC6  1|    |28  PC5 (AI 5)
//      (D 0) PD0  2|    |27  PC4 (AI 4)
//      (D 1) PD1  3|    |26  PC3 (AI 3)
//      (D 2) PD2  4|    |25  PC2 (AI 2)
// PWM+ (D 3) PD3  5|    |24  PC1 (AI 1)
//      (D 4) PD4  6|    |23  PC0 (AI 0)
//            VCC  7|    |22  GND
//            GND  8|    |21  AREF
//            PB6  9|    |20  AVCC
//            PB7 10|    |19  PB5 (D 13)
// PWM+ (D 5) PD5 11|    |18  PB4 (D 12)
// PWM+ (D 6) PD6 12|    |17  PB3 (D 11) PWM
//      (D 7) PD7 13|    |16  PB2 (D 10) PWM
//      (D 8) PB0 14|    |15  PB1 (D  9) PWM
//                  +----+
//
// (PWM+ indicates the additional PWM pins on the ATmega168.)

// ATMEL ATMEGA1280 / ARDUINO  what is this???
//  0- 7 PE0-PE7 works
//  8-13 PB0-PB5 works
// 14-21 PA0-PA7 works 
// 22-29 PH0-PH7 works
// 30-35 PG5-PG0 works
// 36-43 PC7-PC0 works
// 44-51 PJ7-PJ0 works
// 52-59 PL7-PL0 works
// 60-67 PD7-PD0 works
// A0-A7 PF0-PF7
// A8-A15 PK0-PK7 

const uint16_t PROGMEM 
port_to_mode_PGM[]   = { NOT_A_PORT, NOT_A_PORT, &DDRB,  &DDRC,  &DDRD,  };   // why training  comma??(_)
port_to_output_PGM[] = { NOT_A_PORT, NOT_A_PORT, &PORTB, &PORTC, &PORTD, }; 
port_to_input_PGM[]  = { NOT_A_PORT, NOT_A_PORT, &PINB,  &PINC,  &PIND,  }; 

// arrays (indexed by pin "index") map port names (e.g. port B) to the addresses for various functions (reading  and writing)
// hence D,B,C ordering !
digital_pin_to_port_PGM[] = { PD, PD, PD, PD, PD, PD, PD, PD,    PB, PB, PB, PB, PB, PB,     PC, PC, PC, PC, PC, PC, };
/*                             0                           7      8                  13      14                   19
//                            ++++++++++++ 0-7 +++++++++++++++  ++++++++ 0-5 +++++++++++   +++++++++++   0-6 ! +++++++
const uint8_t PROGMEM 
digital_pin_to_bit_mask_PGM[] = { _BV(0), _BV(1), _BV(2), _BV(3), _BV(4), _BV(5), _BV(6), _BV(7),/* 0, port D */
                                  _BV(0), _BV(1), _BV(2), _BV(3), _BV(4), _BV(5), /* 8, port B */
                                  _BV(0), _BV(1), _BV(2), _BV(3), _BV(4), _BV(5), };/* 14, port C */

                                    0             1             2
digital_pin_to_timer_PGM[] = { NOT_ON_TIMER, NOT_ON_TIMER, NOT_ON_TIMER,/* 0 - port D */
                                TIMER2B,     // ATmega168, digital pin 3 has hardware pwm
                                TIMER0B,     // ATmega168, digital pins 5 and 6 have hardware pwm
                                TIMER0A,     // ATmega168, digital pins 5 and 6 have hardware pwm
                                NOT_ON_TIMER, NOT_ON_TIMER, 

                            NOT_ON_TIMER, TIMER1A, TIMER1B, TIMER2, TIMER2A, NOT_ON_TIMER, NOT_ON_TIMER, NOT_ON_TIMER,/* 8 - port B */
                            NOT_ON_TIMER, NOT_ON_TIMER, NOT_ON_TIMER, NOT_ON_TIMER, NOT_ON_TIMER,/* 14 - port C */
};

#endif

/* This DOCUMENT is free software; you can redistribute it and/or modify it under the terms of the GNU Lesser General Public
  License as published by the Free Software Foundation; either version 2.1 of the License, or (at your option) any later version.

  This library is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public License for more details.

  You should have received a copy of the GNU Lesser General Public License along with this library; if not, write to the
  Free Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA

  $Id: wiring.h 249 2007-02-03 16:52:51Z mellis $ */