;;
  ;;  mur.sat
  ;;
  ;;  Somewhen in the year 20xx, mur.at will have a nano satellite launched
  ;;  into a low earth orbit (310 km above the surface of our planet). The
  ;;  satellite itself is a TubeSat personal satellite kit, developed and
  ;;  launched by interorbital systems. mur.sat is a joint venture of mur.at,
  ;;  ESC im Labor and realraum.
  ;;
  ;;  Please visit the project hompage at sat.mur.at for further information.
  ;; 
  ;;
  ;;  Copyright (C) 2011-2015 Christian Pointner <equinox@mur.at>
  ;;                         
  ;;  This file is part of mur.sat.
  ;;
  ;;  mur.sat is free software: you can redistribute it and/or modify
  ;;  it under the terms of the GNU General Public License as published by
  ;;  the Free Software Foundation, either version 3 of the License, or
  ;;  any later version.
  ;;
  ;;  mur.sat 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 General Public License for more details.
  ;;
  ;;  You should have received a copy of the GNU General Public License
  ;;  along with mur.sat. If not, see <http://www.gnu.org/licenses/>.
  ;;

  ;; -------------------------------------
i2c_start
  movlb     .1
  bcf       I2C_SDA
  nop
  bcf       I2C_SCL
  movlb     .0
  return
  
  ;; ------------------
i2c_restart
  movlb     .1
  bsf       I2C_SDA
  nop
  bsf       I2C_SCL
  nop
  nop
  nop
  bcf       I2C_SDA
  nop
  bcf       I2C_SCL
  movlb     .0
  return
  
  ;; ------------------
i2c_stop
  movlb     .1
  bsf       I2C_SCL
  nop
  bsf       I2C_SDA
  movlb     .0
  return
  
  ;; ------------------
i2c_send_byte
  movwf     I2C_BYTE
  movlw     .8
  movwf     I2C_BIT_CNT
  movlb     .1
i2c_send_byte_next
  btfss     I2C_BYTE,7
  bcf       I2C_SDA
  btfsc     I2C_BYTE,7
  bsf       I2C_SDA
  nop
  bsf       I2C_SCL
  nop
  nop
  bcf       I2C_SCL
  rlf       I2C_BYTE,f
  decfsz    I2C_BIT_CNT,f
  goto      i2c_send_byte_next

  nop
  nop
  bsf       I2C_SDA
  bsf       I2C_SCL
  movlb     .0
  movf      PORTB,w
  movlb     .1
  bcf       I2C_SCL
  bcf       I2C_SDA
  movlb     .0
  andlw     b'00010000'
  movwf     I2C_BYTE
  swapf     I2C_BYTE,f
  return

  ;; ------------------
i2c_recv_byte
  clrf      I2C_BYTE
  movlw     .8
  movwf     I2C_BIT_CNT
  movlb     .1
  bsf       I2C_SDA
i2c_recv_byte_loop
  bsf       I2C_SCL
  movlb     .0
  btfsc     I2C_SDA
  bsf       I2C_BYTE,0
  movlb     .1
  bcf       I2C_SCL
  decfsz    I2C_BIT_CNT,f
  goto      i2c_recv_byte_next

  bcf       I2C_SDA
  movlb     .0
  return

i2c_recv_byte_next
  bcf       STATUS,C
  rlf       I2C_BYTE,f
  goto      i2c_recv_byte_loop

  ;; ------------------
i2c_ack
  movlb     .1
  bcf       I2C_SDA
  bsf       I2C_SCL
  nop
  nop
  bcf       I2C_SCL
  movlb     .0
  return
  
  ;; ------------------
i2c_nack
  movlb     .1
  bsf       I2C_SDA
  bsf       I2C_SCL
  nop
  nop
  bcf       I2C_SCL
  bcf       I2C_SDA
  movlb     .0
  return

  ;; -------------------------------------