PCA930——I2C level conversion
The PCA9306 is a bidirectional I2C bus and SMBus voltage level translator with an enable (EN) input that can level shift from 1.0 V to 3.6 V and 1.8 V to 5.5V.
The PCA9306 allows bidirectional voltage conversion between 1.0 V and 5V without using the direction pin. The switch's low on-state resistance (Ron) allows connections with minimal propagation delay. When EN is HIGH, the converter switch is open and the SCL1 and SDA1 I/Os are connected to the SCL2 and SDA2 I/Os respectively, allowing bidirectional data flow between the ports. When EN is low, the converter switch is closed and a high impedance state exists between the ports.
The PCA9306 is not a bus buffer like the PCA9509 or PCA9517A, it provides level shifting and physical isolation to the capacitors on either side of the bus. The PCA9306 only isolates the two sides when the device is disabled and provides voltage level translation when activated. It can also be used to run two buses, one operating at 400 kHz and the other at 100 kHz. If the two buses run at different frequencies, the 100 kHz bus must be isolated when the other bus requires 400 kHz operation. If the main server is running at 400 kHz, then the maximum operating frequency of the system may be less than 400 kHz due to the added latency of the converters. As with standard I2C bus systems, pull-up resistors are required to provide a logic high level on the converter's bus. The PCA9306 has a standard open collector configuration for the I2C bus. The size of these pull-up resistors depends on the system, but there must be one on each side of the converter. In addition to SMBus devices, this device also works with standard mode, fast mode and fast mode+i2c bus devices. The maximum frequency depends on the RC time constant, but >2 MHz is generally supported.
Instructions for use of PCA9306
When the SDA1 or SDA2 port is low, the clamp is ON and there is a low resistance connection between the SDA1 and SDA2 ports. Assuming that the voltage on the SDA2 port is higher when the SDA2 port is higher, the voltage on the SDA1 port is limited to the voltage set by VREF1. When the SDA1 port voltage is high, the SDA2 port will be pulled up to the drain pull-up supply voltage (Vpu (D)) by the pull-up resistor. This feature allows users to seamlessly transition between selected high and low voltages without the need for directional control. The SCL1/SCL2 channels are also used as SDA1/SDA2 channels.
I2C level conversion - 3.3V to 1.8V
The PCA9306 does not provide simultaneous two-level switching on either side of the bus buffer and physical capacitive isolation when both sides are connected. The PCA9306 only isolates the two ends when the device is disabled and provides voltage level translation when activated. In a level translation in the 3.3 V to 1.8 V direction, no pull-up resistor is needed on the 3.3 V side if the 3.3 V side is being driven by a totem pole driver. The relative length of the capacitor and line is on the 1.8 V side because it is driven through the on-resistance of the PCA9306. If the wire length is long enough at the 1.8 V end, the transition time to the chip/terminal where the wire is bonded is shorter than the wire's flight time because the PCA9306 looks like a high impedance wire in comparison. If the wire is not too long and the lumped capacitance signal is only slightly attenuated by the added series resistance through the PCA9306. If the lumped capacitance is large, the rise time will deteriorate, the fall time is much less affected, if the rise time is too slow the clock's duty cycle will be degraded, and at some point the clock will no longer be useful. Therefore, design considerations are to minimize trace length and capacitance on one side of the 1.8 V clock path. The pull-up resistor at the 1.8 V end can also be used to exchange a slower fall time for a faster rise and in some cases can reduce overshoot, so changing the corresponding voltage regulator chip can achieve 3.3V to 1.8V.
Sample code
#include "stm32f10x.h"
#include "OLED_Font.h"
/*引脚配置*/
#define OLED_W_SCL(x) GPIO_WriteBit(GPIOB, GPIO_Pin_8, (BitAction)(x))
#define OLED_W_SDA(x) GPIO_WriteBit(GPIOB, GPIO_Pin_9, (BitAction)(x))
/*引脚初始化*/
void OLED_I2C_Init(void)
{
RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOB, ENABLE);
GPIO_InitTypeDef GPIO_InitStructure;
GPIO_InitStructure.GPIO_Mode = GPIO_Mode_Out_OD;
GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
GPIO_InitStructure.GPIO_Pin = GPIO_Pin_8;
GPIO_Init(GPIOB, &GPIO_InitStructure);
GPIO_InitStructure.GPIO_Pin = GPIO_Pin_9;
GPIO_Init(GPIOB, &GPIO_InitStructure);
OLED_W_SCL(1);
OLED_W_SDA(1);
}
/**
* @brief I2C开始
* @param 无
* @retval 无
*/
void OLED_I2C_Start(void)
{
OLED_W_SDA(1);
OLED_W_SCL(1);
OLED_W_SDA(0);
OLED_W_SCL(0);
}
/**
* @brief I2C停止
* @param 无
* @retval 无
*/
void OLED_I2C_Stop(void)
{
OLED_W_SDA(0);
OLED_W_SCL(1);
OLED_W_SDA(1);
}
/**
* @brief I2C发送一个字节
* @param Byte 要发送的一个字节
* @retval 无
*/
void OLED_I2C_SendByte(uint8_t Byte)
{
uint8_t i;
for (i = 0; i < 8; i++)
{
OLED_W_SDA(Byte & (0x80 >> i));
OLED_W_SCL(1);
OLED_W_SCL(0);
}
OLED_W_SCL(1); //额外的一个时钟，不处理应答信号
OLED_W_SCL(0);
}
/**
* @brief OLED写命令
* @param Command 要写入的命令
* @retval 无
*/
void OLED_WriteCommand(uint8_t Command)
{
OLED_I2C_Start();
OLED_I2C_SendByte(0x78); //从机地址
OLED_I2C_SendByte(0x00); //写命令
OLED_I2C_SendByte(Command);
OLED_I2C_Stop();
}
/**
* @brief OLED写数据
* @param Data 要写入的数据
* @retval 无
*/
void OLED_WriteData(uint8_t Data)
{
OLED_I2C_Start();
OLED_I2C_SendByte(0x78); //从机地址
OLED_I2C_SendByte(0x40); //写数据
OLED_I2C_SendByte(Data);
OLED_I2C_Stop();
}
/**
* @brief OLED设置光标位置
* @param Y 以左上角为原点，向下方向的坐标，范围：0~7
* @param X 以左上角为原点，向右方向的坐标，范围：0~127
* @retval 无
*/
void OLED_SetCursor(uint8_t Y, uint8_t X)
{
OLED_WriteCommand(0xB0 | Y); //设置Y位置
OLED_WriteCommand(0x10 | ((X & 0xF0) >> 4)); //设置X位置高4位
OLED_WriteCommand(0x00 | (X & 0x0F)); //设置X位置低4位
}
/**
* @brief OLED清屏
* @param 无
* @retval 无
*/
void OLED_Clear(void)
{
uint8_t i, j;
for (j = 0; j < 8; j++)
{
OLED_SetCursor(j, 0);
for(i = 0; i < 128; i++)
{
OLED_WriteData(0x00);
}
}
}
/**
* @brief OLED显示一个字符
* @param Line 行位置，范围：1~4
* @param Column 列位置，范围：1~16
* @param Char 要显示的一个字符，范围：ASCII可见字符
* @retval 无
*/
void OLED_ShowChar(uint8_t Line, uint8_t Column, char Char)
{
uint8_t i;
OLED_SetCursor((Line - 1) * 2, (Column - 1) * 8); //设置光标位置在上半部分
for (i = 0; i < 8; i++)
{
OLED_WriteData(OLED_F8x16[Char - ' '][i]); //显示上半部分内容
}
OLED_SetCursor((Line - 1) * 2 + 1, (Column - 1) * 8); //设置光标位置在下半部分
for (i = 0; i < 8; i++)
{
OLED_WriteData(OLED_F8x16[Char - ' '][i + 8]); //显示下半部分内容
}
}
/**
* @brief OLED显示字符串
* @param Line 起始行位置，范围：1~4
* @param Column 起始列位置，范围：1~16
* @param String 要显示的字符串，范围：ASCII可见字符
* @retval 无
*/
void OLED_ShowString(uint8_t Line, uint8_t Column, char *String)
{
uint8_t i;
for (i = 0; String[i] != '\0'; i++)
{
OLED_ShowChar(Line, Column + i, String[i]);
}
}
/**
* @brief OLED次方函数
* @retval 返回值等于X的Y次方
*/
uint32_t OLED_Pow(uint32_t X, uint32_t Y)
{
uint32_t Result = 1;
while (Y--)
{
Result *= X;
}
return Result;
}
/**
* @brief OLED显示数字（十进制，正数）
* @param Line 起始行位置，范围：1~4
* @param Column 起始列位置，范围：1~16
* @param Number 要显示的数字，范围：0~4294967295
* @param Length 要显示数字的长度，范围：1~10
* @retval 无
*/
void OLED_ShowNum(uint8_t Line, uint8_t Column, uint32_t Number, uint8_t Length)
{
uint8_t i;
for (i = 0; i < Length; i++)
{
OLED_ShowChar(Line, Column + i, Number / OLED_Pow(10, Length - i - 1) % 10 + '0');
}
}
/**
* @brief OLED显示数字（十进制，带符号数）
* @param Line 起始行位置，范围：1~4
* @param Column 起始列位置，范围：1~16
* @param Number 要显示的数字，范围：-2147483648~2147483647
* @param Length 要显示数字的长度，范围：1~10
* @retval 无
*/
void OLED_ShowSignedNum(uint8_t Line, uint8_t Column, int32_t Number, uint8_t Length)
{
uint8_t i;
uint32_t Number1;
if (Number >= 0)
{
OLED_ShowChar(Line, Column, '+');
Number1 = Number;
}
else
{
OLED_ShowChar(Line, Column, '-');
Number1 = -Number;
}
for (i = 0; i < Length; i++)
{
OLED_ShowChar(Line, Column + i + 1, Number1 / OLED_Pow(10, Length - i - 1) % 10 + '0');
}
}
/**
* @brief OLED显示数字（十六进制，正数）
* @param Line 起始行位置，范围：1~4
* @param Column 起始列位置，范围：1~16
* @param Number 要显示的数字，范围：0~0xFFFFFFFF
* @param Length 要显示数字的长度，范围：1~8
* @retval 无
*/
void OLED_ShowHexNum(uint8_t Line, uint8_t Column, uint32_t Number, uint8_t Length)
{
uint8_t i, SingleNumber;
for (i = 0; i < Length; i++)
{
SingleNumber = Number / OLED_Pow(16, Length - i - 1) % 16;
if (SingleNumber < 10)
{
OLED_ShowChar(Line, Column + i, SingleNumber + '0');
}
else
{
OLED_ShowChar(Line, Column + i, SingleNumber - 10 + 'A');
}
}
}
/**
* @brief OLED显示数字（二进制，正数）
* @param Line 起始行位置，范围：1~4
* @param Column 起始列位置，范围：1~16
* @param Number 要显示的数字，范围：0~1111 1111 1111 1111
* @param Length 要显示数字的长度，范围：1~16
* @retval 无
*/
void OLED_ShowBinNum(uint8_t Line, uint8_t Column, uint32_t Number, uint8_t Length)
{
uint8_t i;
for (i = 0; i < Length; i++)
{
OLED_ShowChar(Line, Column + i, Number / OLED_Pow(2, Length - i - 1) % 2 + '0');
}
}
/**
* @brief OLED初始化
* @param 无
* @retval 无
*/
void OLED_Init(void)
{
uint32_t i, j;
for (i = 0; i < 1000; i++) //上电延时
{
for (j = 0; j < 1000; j++);
}
OLED_I2C_Init(); //端口初始化
OLED_WriteCommand(0xAE); //关闭显示
OLED_WriteCommand(0xD5); //设置显示时钟分频比/振荡器频率
OLED_WriteCommand(0x80);
OLED_WriteCommand(0xA8); //设置多路复用率
OLED_WriteCommand(0x3F);
OLED_WriteCommand(0xD3); //设置显示偏移
OLED_WriteCommand(0x00);
OLED_WriteCommand(0x40); //设置显示开始行
OLED_WriteCommand(0xA1); //设置左右方向，0xA1正常 0xA0左右反置
OLED_WriteCommand(0xC8); //设置上下方向，0xC8正常 0xC0上下反置
OLED_WriteCommand(0xDA); //设置COM引脚硬件配置
OLED_WriteCommand(0x12);
OLED_WriteCommand(0x81); //设置对比度控制
OLED_WriteCommand(0xCF);
OLED_WriteCommand(0xD9); //设置预充电周期
OLED_WriteCommand(0xF1);
OLED_WriteCommand(0xDB); //设置VCOMH取消选择级别
OLED_WriteCommand(0x30);
OLED_WriteCommand(0xA4); //设置整个显示打开/关闭
OLED_WriteCommand(0xA6); //设置正常/倒转显示
OLED_WriteCommand(0x8D); //设置充电泵
OLED_WriteCommand(0x14);
OLED_WriteCommand(0xAF); //开启显示
OLED_Clear(); //OLED清屏
}
#include "stm32f10x.h" // Device header
#include "Delay.h"
#include "OLED.h"
int main(void)
{
OLED_Init();
OLED_ShowString(1, 1, "Hello World!");
while (1)
{
}
}