910 QuadPulse — 4-Channel Servo/Motor PWM ASIC
910 : QuadPulse — 4-Channel Servo/Motor PWM ASIC
- Author: Sarvesh S
- Description: A dedicated 4-channel PWM generator ASIC for servo and DC motor control in robotic systems. Eliminates software timing jitter by implementing PWM generation entirely in silicon. Supports 50 Hz servo control through 20 kHz motor drive. SPI interface allows runtime duty cycle updates from any microcontroller. Hardware emergency stop instantly silences all channels. Designed for autonomous robotic swarm applications where deterministic multi-channel motor control is critical.
- GitHub repository
- Open in 3D viewer
- Clock: 10000000 Hz
How it works
QuadPulse generates 4 independent, jitter-free PWM signals for servo and DC motor control. It uses a 10 MHz system clock divided into a configurable PWM period, with a phase accumulator ramp giving 8-bit (256-step) duty cycle resolution at all frequencies.
A 3-wire SPI interface accepts 16-bit frames (2-bit channel address + 8-bit duty value) to load duty cycles at runtime without CPU involvement. A hardware emergency stop pin (ui_in[0]) instantly forces all outputs to zero via combinational logic — no latency.
All SPI inputs pass through 2-stage flip-flop synchronisers to prevent metastability from the asynchronous SPI clock domain. The frequency selector is registered to suppress DIP switch bounce. Four frequency modes are supported: 50 Hz (hobby servos), 1 kHz, 10 kHz, and 20 kHz (silent motor drivers).
How to test
Set the frequency with ui_in[2:1]: 00=50 Hz, 01=1 kHz, 10=10 kHz, 11=20 kHz.
Send a 16-bit SPI frame via uio[0] (MOSI), uio[1] (SCLK), uio[2] (CS_N active-low):
- Bits [15:14]: channel address (00=CH0, 01=CH1, 10=CH2, 11=CH3)
- Bits [13:8]: reserved (send as 0)
- Bits [7:0]: duty cycle (0=0%, 127=50%, 255=100%)
Observe PWM outputs on uo_out[3:0]. Connect an LED through a 470 ohm resistor to uo_out[0] to see duty cycle as brightness without an oscilloscope. Set ui_in[0]=1 to trigger emergency stop (all outputs go to 0 immediately, uo_out[4] goes HIGH).
Run the cocotb simulation test suite with cd test && make
External hardware
- Hobby servo (SG90 or equivalent) on uo_out[0..3] at 50 Hz
- DC motor + PWM driver module (e.g., L298N) at 1-20 kHz
- LED + 470 ohm resistor for visual duty cycle demo (no oscilloscope needed)
- Any MCU (STM32, ESP32, RP2040) as SPI master
IO
| # | Input | Output | Bidirectional |
|---|---|---|---|
| 0 | Emergency Stop — HIGH forces all PWM outputs to 0 | PWM Channel 0 output (Servo 1 / Motor 1) | SPI MOSI — serial data from microcontroller to chip |
| 1 | Freq select bit 0 — 00=50Hz 01=1kHz 10=10kHz 11=20kHz | PWM Channel 1 output (Servo 2 / Motor 2) | SPI SCLK — SPI clock from microcontroller |
| 2 | Freq select bit 1 | PWM Channel 2 output (Servo 3 / Motor 3) | SPI CS_N — chip select, active LOW |
| 3 | PWM Channel 3 output (Servo 4 / Motor 4) | ||
| 4 | Emergency Stop flag — HIGH when emergency stop is active | ||
| 5 | |||
| 6 | |||
| 7 |