This is an 8-channel PWM controller for LED brightness.
The PWM duty cycle is generated according to an X<sup>3</sup> curve, so the "percieved brightness" changes linearly with the register setting. This design means we get the dynamic range of a 16-bit PWM but use only 8 bits to specify the desired output. With an input clock of 32.7 MHz, the PWM frequency is 500 Hz.
After reset, the controller is in UI mode, where the ui[7:0] set the 8 PWM value registers. The first PWM value register is set to ui[7:0], for the remaining PWM value registers they are set to 0 when ui[7:0] == 0, but in other cases their value is ui[7:0] XOR X, where X is 0x10 times the register number.
The individual registers can be accessed by I2C; SCL=UIO2, SDA=UIO1, which should allow accessing it from the Rpi2040 on the demo board. The slave address is 0x6C, and the 8 PWM channels are controlled by register addresses 0 thru 7. As soon as the first I2C write occurs, the controller is set to I2C mode, and the ui inputs no longer affect the registers.
Play with the DIP-switches to see different segments of the 7-segment LED display show different brightnesses.
Currently no external hardware is supported.
| # | Input | Output | Bidirectional |
|---|---|---|---|
| 0 | duty[0] | PWM channel 0 | |
| 1 | duty[1] | PWM channel 1 | SDA |
| 2 | duty[2] | PWM channel 2 | SCL |
| 3 | duty[3] | PWM channel 3 | |
| 4 | duty[4] | PWM channel 4 | |
| 5 | duty[5] | PWM channel 5 | |
| 6 | duty[6] | PWM channel 6 | |
| 7 | duty[7] | PWM channel 7 |