Mixed voltage interfacing with the Bus Pirate

From DP

This will be an updated guide to using the Bus Pirate pull-up resistors to interface stuff at different voltages.

About

The Bus Pirate's on-board pull-up resistors can be used to interface electronics above and below the Bus Pirate's 3.3volt supply.

Read how the pull-up resistors on the Bus Pirate work.

Read our guide to pull-up resistors and high impedance pins.

Examples

Here's some examples of how to interface different voltages using the Bus Pirate.

These examples assume you use the Bus Pirate on-board pullup resistors. If you use the Bus Pirate's on-board pull-up resistors, remember to connect the Vpullup pin to the circuit supply voltage. The Bus Pirate pull-up resistors are powered through the Vpullup pin.

Some modes (1-Wire, I2C) only use high impedance pin outputs

3.3volts

Select output type:
1. Open drain (H=Hi-Z, L=GND)
2. Normal (H=3.3V, L=GND)

(1)> 2
Ready

• Interface directly with normal pin outputs
• No pull-ups or Vpullup pin connection used

5.0volts

Select output type:
1. Open drain (H=Hi-Z, L=GND)
2. Normal (H=3.3V, L=GND)

(1)> 1
Ready
SPI> W
Power supplies ON
SPI> P
Pull-up resistors ON

• Connect the Vpullup pin to the power supply of the 5volt circuit
• Choose Hi-Z output type
• Enable the on-board pull-up resistors
• The 5volts can come from the Bus Pirate or an external supply

2.5volts

Select output type:
1. Open drain (H=Hi-Z, L=GND)
2. Normal (H=3.3V, L=GND)

(1)> 1
Ready
SPI> P
Pull-up resistors ON

• Choose Hi-Z output type
• Connect the Vpullup pin to the power supply of the 2.5volt circuit

Any voltage 1-Wire, I2C

I2C> P
Pull-up resistors ON

• The Bus Pirate can interface with 1-Wire or I2C at 5.5volts or less
• Open collector buses like 1-Wire and I2C always use pull-up resistors
• These modes have no output configuration, outputs are always HiZ