diff --git a/examples/i2c_slave/Makefile b/examples/i2c_slave/Makefile
new file mode 100644
index 0000000000000000000000000000000000000000..49b91ce536597c14d0d8273010cba332c68baef1
--- /dev/null
+++ b/examples/i2c_slave/Makefile
@@ -0,0 +1,9 @@
+all : flash
+
+TARGET:=i2c_slave
+
+include ../../ch32v003fun/ch32v003fun.mk
+
+flash : cv_flash
+clean : cv_clean
+
diff --git a/examples/i2c_slave/README.md b/examples/i2c_slave/README.md
new file mode 100644
index 0000000000000000000000000000000000000000..cfdbd1b46fb2f58e9bea2c7b4ce8d2aa0e4ee367
--- /dev/null
+++ b/examples/i2c_slave/README.md
@@ -0,0 +1,9 @@
+# I2C peripheral in slave mode
+
+This library and example show how to use the I2C peripheral in slave mode.
+
+The library uses a one-byte address, allowing for up to 256 registers to be defined.
+
+The first byte written to the device within a transaction determines the offset for following reads and writes, emulating a simple EEPROM.
+
+The example will turn on a LED connected to PD0 when the LSB of register 0 is set to 1 and off when it's set to 0.
diff --git a/examples/i2c_slave/i2c_slave.c b/examples/i2c_slave/i2c_slave.c
new file mode 100644
index 0000000000000000000000000000000000000000..dbfaf80ec8448a67b4f5ab3e5ece38b1bb6c02d3
--- /dev/null
+++ b/examples/i2c_slave/i2c_slave.c
@@ -0,0 +1,30 @@
+#define SYSTEM_CORE_CLOCK 48000000
+
+#include "ch32v003fun.h"
+#include "i2c_slave.h"
+#include <stdio.h>
+
+// The I2C slave library uses a one byte address so you can extend the size of this array up to 256 registers
+// note that the register set is modified by interrupts, to prevent the compiler from accidently optimizing stuff
+// away make sure to declare the register array volatile
+
+volatile uint8_t i2c_registers[32] = {0x00};
+
+int main() {
+ SystemInit48HSI();
+ SetupDebugPrintf();
+ SetupI2CSlave(0x9, i2c_registers, sizeof(i2c_registers));
+
+ // Enable GPIOD and set pin 0 to output
+ RCC->APB2PCENR |= RCC_APB2Periph_GPIOD;
+ GPIOD->CFGLR &= ~(0xf<<(4*0));
+ GPIOD->CFGLR |= (GPIO_Speed_10MHz | GPIO_CNF_OUT_PP)<<(4*0);
+
+ while (1) {
+ if (i2c_registers[0] & 1) { // Turn on LED (PD0) if bit 1 of register 0 is set
+ GPIOD-> BSHR |= 1 << 16;
+ } else {
+ GPIOD-> BSHR |= 1;
+ }
+ }
+}
diff --git a/examples/i2c_slave/i2c_slave.h b/examples/i2c_slave/i2c_slave.h
new file mode 100644
index 0000000000000000000000000000000000000000..a488eaf8ea046d5ca80e395a2715650d9213dbeb
--- /dev/null
+++ b/examples/i2c_slave/i2c_slave.h
@@ -0,0 +1,150 @@
+/*
+ * Single-File-Header for using the I2C peripheral in slave mode
+ *
+ * MIT License
+ *
+ * Copyright (c) 2023 Renze Nicolai
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+
+#ifndef __I2C_SLAVE_H
+#define __I2C_SLAVE_H
+
+#include <stdint.h>
+
+#define APB_CLOCK SYSTEM_CORE_CLOCK
+
+struct _i2c_slave_state {
+ uint8_t first_write;
+ uint8_t offset;
+ uint8_t position;
+ volatile uint8_t* volatile registers;
+ uint8_t size;
+} i2c_slave_state;
+
+void SetupI2CSlave(uint8_t address, volatile uint8_t* registers, uint8_t size) {
+ i2c_slave_state.first_write = 1;
+ i2c_slave_state.offset = 0;
+ i2c_slave_state.position = 0;
+ i2c_slave_state.registers = registers;
+ i2c_slave_state.size = size;
+
+ // Enable GPIOC and I2C
+ RCC->APB2PCENR |= RCC_APB2Periph_GPIOC;
+ RCC->APB1PCENR |= RCC_APB1Periph_I2C1;
+
+ // PC1 is SDA, 10MHz Output, alt func, open-drain
+ GPIOC->CFGLR &= ~(0xf<<(4*1));
+ GPIOC->CFGLR |= (GPIO_Speed_10MHz | GPIO_CNF_OUT_OD_AF)<<(4*1);
+
+ // PC2 is SCL, 10MHz Output, alt func, open-drain
+ GPIOC->CFGLR &= ~(0xf<<(4*2));
+ GPIOC->CFGLR |= (GPIO_Speed_10MHz | GPIO_CNF_OUT_OD_AF)<<(4*2);
+
+ // Reset I2C1 to init all regs
+ RCC->APB1PRSTR |= RCC_APB1Periph_I2C1;
+ RCC->APB1PRSTR &= ~RCC_APB1Periph_I2C1;
+
+ I2C1->CTLR1 |= I2C_CTLR1_SWRST;
+ I2C1->CTLR1 &= ~I2C_CTLR1_SWRST;
+
+ // Set module clock frequency
+ uint32_t prerate = 2000000; // I2C Logic clock rate, must be higher than the bus clock rate
+ I2C1->CTLR2 |= (APB_CLOCK/prerate) & I2C_CTLR2_FREQ;
+
+ // Enable interrupts
+ I2C1->CTLR2 |= I2C_CTLR2_ITBUFEN;
+ I2C1->CTLR2 |= I2C_CTLR2_ITEVTEN; // Event interrupt
+ I2C1->CTLR2 |= I2C_CTLR2_ITERREN; // Error interrupt
+
+ NVIC_EnableIRQ(I2C1_EV_IRQn); // Event interrupt
+ NVIC_SetPriority(I2C1_EV_IRQn, 2 << 4);
+ NVIC_EnableIRQ(I2C1_ER_IRQn); // Error interrupt
+
+ // Set clock configuration
+ uint32_t clockrate = 1000000; // I2C Bus clock rate, must be lower than the logic clock rate
+ I2C1->CKCFGR = ((APB_CLOCK/(3*clockrate))&I2C_CKCFGR_CCR) | I2C_CKCFGR_FS; // Fast mode 33% duty cycle
+ //I2C1->CKCFGR = ((APB_CLOCK/(25*clockrate))&I2C_CKCFGR_CCR) | I2C_CKCFGR_DUTY | I2C_CKCFGR_FS; // Fast mode 36% duty cycle
+ //I2C1->CKCFGR = (APB_CLOCK/(2*clockrate))&I2C_CKCFGR_CCR; // Standard mode good to 100kHz
+
+ // Set I2C address
+ I2C1->OADDR1 = address << 1;
+
+ // Enable I2C
+ I2C1->CTLR1 |= I2C_CTLR1_PE;
+
+ // Acknowledge the first address match event when it happens
+ I2C1->CTLR1 |= I2C_CTLR1_ACK;
+}
+
+void I2C1_EV_IRQHandler(void) __attribute__((interrupt));
+void I2C1_EV_IRQHandler(void) {
+ uint16_t STAR1, STAR2 __attribute__((unused));
+ STAR1 = I2C1->STAR1;
+ STAR2 = I2C1->STAR2;
+
+ I2C1->CTLR1 |= I2C_CTLR1_ACK;
+
+ if (STAR1 & I2C_STAR1_ADDR) { // Start event
+ i2c_slave_state.first_write = 1; // Next write will be the offset
+ i2c_slave_state.position = i2c_slave_state.offset; // Reset position
+ }
+
+ if (STAR1 & I2C_STAR1_RXNE) { // Write event
+ if (i2c_slave_state.first_write) { // First byte written, set the offset
+ i2c_slave_state.offset = I2C1->DATAR;
+ i2c_slave_state.position = i2c_slave_state.offset;
+ i2c_slave_state.first_write = 0;
+ } else { // Normal register write
+ if (i2c_slave_state.position < i2c_slave_state.size) {
+ i2c_slave_state.registers[i2c_slave_state.position] = I2C1->DATAR;
+ i2c_slave_state.position++;
+ }
+ }
+ }
+
+ if (STAR1 & I2C_STAR1_TXE) { // Read event
+ if (i2c_slave_state.position < i2c_slave_state.size) {
+ I2C1->DATAR = i2c_slave_state.registers[i2c_slave_state.position];
+ i2c_slave_state.position++;
+ } else {
+ I2C1->DATAR = 0x00;
+ }
+ }
+}
+
+void I2C1_ER_IRQHandler(void) __attribute__((interrupt));
+void I2C1_ER_IRQHandler(void) {
+ uint16_t STAR1 = I2C1->STAR1;
+
+ if (STAR1 & I2C_STAR1_BERR) { // Bus error
+ I2C1->STAR1 &= ~(I2C_STAR1_BERR); // Clear error
+ }
+
+ if (STAR1 & I2C_STAR1_ARLO) { // Arbitration lost error
+ I2C1->STAR1 &= ~(I2C_STAR1_ARLO); // Clear error
+ }
+
+ if (STAR1 & I2C_STAR1_AF) { // Acknowledge failure
+ I2C1->STAR1 &= ~(I2C_STAR1_AF); // Clear error
+ }
+}
+
+#endif