pHAT Module Series

pHAT-RV Technical Description

pHAT-RV Technical Description

Page 21 of 27

position is reached. These many sub-positions ensure that the mechanical position closely

relates to the position requested by the pulse width and therefore the determination of final

position (movement complete) will closely relate to mechanical position. As servo speed is

increased the error between mechanical position and pulse width position increases and

movement completion accuracy is degraded.

3.7.9 I

2C Global Update Register

Once all the required position & control registers have been set a write to the 0x19hex (Global

update) must be made to activate all the new positions.

3.7.10 I

2C Write Example

To step stepper motor 1 500 half-steps clockwise at 3mS per step and then hold in that

position and servo 1 to position 30 running at speed 0 write:

Byte 1 (RV Adr)

11101000binary

Byte 2 (Register 0)

0decimal

Byte 3 (Register 1)

25decimal, 19hex

Byte 4 (Register 2)

1decimal, 01hex

Byte 5 (Register 3)

232decimal, E8hex

Byte 6 (Register 4)

12decimal, 0Chex

Then write:

Byte 1 (RV Adr)

11101000binary

Byte 2 (Register 0)

17decimal

Byte 3 (Register 17)

30decimal, 1Ehex

Byte 4 (Register 18)

144decimal, 90hex

Then to activate write:

Byte 1 (RV Adr)

11101000binary

Byte 2 (Register 0)

25decimal

Byte 3 (Register 25)

0decimal

3.8 Application Software

3.8.1 Demonstration Software

Raspberry-Pi demonstration software written in Python is available to download from the

website www.designersystems.co.uk/robotics