The 1-Wire port is based around a DS2482-100 I2C to 1-Wire bridge device. The DS2482-100 provides bi-directional protocol conversion between the I2C port on the Raspberry Pi and any attached 1-Wire® slave devices. An ESD Protection Diode is used to protect the Board and Raspberry Pi from electrostatic spikes on the 1-Wire port. Connections to the 1-Wire port can be made through pin on the PCB. 

1. J2 J3  Step motor connector J2 (5V,D0,D1,D2,D3)  J3(5V,D4,D5,D6,D7) 

      can use Step motor (28BYJ-48 5VDC)48 5VDC)48 5VDC)48 5VDC)8 5VDC)

2. J20   5V,GND, D0, D1,D2,D3,D4,D5,D6,D7   OUTPUT

3. U5 ULN2803 8 darlington transistor array

4. J17  RS-Pi-V2 GPIO output      

5. J19  i2c output (GND,5V,SDA,SCL)

6.  JP4 choose 5V input from Mini USB Port J7 or RS-Pi 5V

7. J7  Mini USB 5V input

8. U6 MCP3002 SPI Interface  10 bit Analog-to-Digital Converter 

     output   J11  (Vcc, AD0, GND, AD1)       MCP3002 Data Sheet

9. U11 MCP4802  SPI Interface 8 bit Digital-to-Analog Converter   

      or U11 MCP4812 SPI Interface 10 bit Digital-to-Analog Converter   

      or  U11 MCP4822 SPI Interface 12 bit Digital-to-Analog Converter   

      output JP1 (DA0,GND,DA1,GND)            MCP4802 Data Sheet

You can choose 8 bit , 10bit or 12 bit  DAC ,

10. U15 DS2482-100 I2C to 1-Wire bridge device      DS2482-100  Data Sheet

     J22 1-wire Port pin 1 - pin4 

     (5V,GND, OW (1-Wire Data, ESD Protected). RT (1-Wire Return/Ground ,ESC protected)

11. U16 DS9503P ESD protection diode

12. D8,D9, D10, D11  GPIO 28,29,30.31 output LED

    U5 uln2803  use  RS-Pi  pin 11,12,13,15,16,18,22,7 as GPIO 0 to GPIO7

 Test Program download

SPI AD/DA.c           mcp4802.c