INTERNAL PROTOCOLS AND RABBIT PORT ASSIGNMENTS
==============================================
Started 2014 Aug 29  A.Stummer


****** AD9858/9 SERIAL PROTOCOL **************
1) Set IO_UPDATE low, SDIO3 high, Clk low, !CS high
2) Set SDIO3 low (enables SPI state machine)
3) Set !CS low
4) Set data bit (command address then data, MSB first)
5) Toggle clock high/low
6) Repeat 4-5 for full command
7) Set !CS high to load buffers
8) Repeat for other commands, if any
9) SDIO3 no longer matters, can be used for RU/RD function
10) Toggle IO_UPDATE high/low to implement buffers


***** RABBIT RCM6760 PORT MAPPING ************
PORT  DIR  DESCRIPTION
----------------------------------------------
PA0    -   
PA1    -   
PA2    -   
PA3    -   
PA4    -   
PA5    -   
PA6    -   
PA7    -   

PB0    -   [reserved, flash SCLK]
PB1    -   [reserved, programmer]
PB2    -   
PB3    O   IO_UPDATE
PB4    O   SDIO3
PB5    -
PB6    O   DDS master Reset
PB7    O   DDS Power Down

PC0    IO  DDS SDIO, Touch Data
PC1    O   DDS SCLK
PC2    O   DDS !CS
PC3    O   Display async serial data, TXC
PC4    -   
PC5    -   
PC6    -   [reserved, programmer]
PC7    -   [reserved, programmer]

PD0    -   
PD1    -   
PD2    -   
PD3    -   
PD4    -   [reserved, flash SI]
PD5    -   [reserved, flash SO]
PD6    -   [reserved, flash !CS]
PD7    -   

PE0    -   
PE1    -   
PE2    -   
PE3    -   
PE4    -   
PE5    -
PE6    -
PE7    -