anchor.diff:       6 bit constant RF:IRQ1_RXRDY
        3 bit constant RF:IRQ1_RSSI
        2 bit constant RF:IRQ1_TIMEOUT
  -     0 bit constant RF:IRQ1_SMATCH
  +     0 bit constant RF:IRQ1_SYNC
   
        6 bit constant RF:IRQ2_FIFO_NE
        3 bit constant RF:IRQ2_SENT
        2 bit constant RF:IRQ2_RECVD
  -
  -   0 variable rf.mode
  -   0 variable rf.last
  +     1 bit constant RF:IRQ2_CRCOK
  +
  +   0 variable rf.mode  \ last set chip mode
  +   0 variable rf.last  \ flag used to fetch RSSI only once per packet
      0 variable rf.rssi  \ RSSI signal strength of last reception
      0 variable rf.lna   \ Low Noise Amplifier setting (set by AGC)
      0 variable rf.afc   \ Auto Frequency Control offset
  
positive.code:        $11 constant RF:PA
         $18 constant RF:LNA
         $1F constant RF:AFC
         $21 constant RF:FEI
         $24 constant RF:RSSI
         $27 constant RF:IRQ1
         $28 constant RF:IRQ2
         $2F constant RF:SYN1
         $30 constant RF:SYN2
         $39 constant RF:ADDR
         $3A constant RF:BCAST
         $3C constant RF:THRESH
  
negative.code: 
  create rf:init  \ initialise the radio, each 16-bit word is <reg#,val>
  hex
    0200 h, \ packet mode, fsk
    0302 h, 048A h, \ bit rate 49,261 hz
    0505 h, 06C3 h, \ 90.3kHzFdev -> modulation index = 2
  