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README
Apache-2.0

前言

最近一个项目用到了LCD段码屏,也是第一次接触,于是花了几天时间研究了一下,于是写下这篇文章与大家交流分享一下。

段码屏显示原理

段码屏的引脚一般分为COM和SEG,COM是公共端,SEG是区段。段码屏显示和熄灭的原理是在对应的RAM地址中写1和0。因此我们需要知道COM和SEG的对应关系。 alt text 如上图所示,这是段码屏上的数码管,着重看第一个数码管,有7段,分别为A、B、C、D、E、F、G。 alt text 如上图COM-SEG对应关系,可知2A对应的是COM3和SEG5。COM-SEG相当是一个坐标,如果想点亮段码屏的某一个位置,需要找到其对应的COM-SEG。比如点亮2D,需要找到SEG5这个区段将COM0置1。

段码屏驱动

IO连接

段码屏的显示原理搞明白了后,那如何驱动他呢,这里采用了HT1621驱动芯片进行驱动。 alt text 如图是HT1621的RAM到COM-SEG映射表,最大支持4X32的数据存储,最多可以控制128个显示点位的段码屏。 alt text 如图可知,其与MCU之间的通信最少需要三线即可,分别是CS(片选信号,低电平有效)、WR(写入时钟信号,上升沿时写入)、DATA(数据信号)。 其与段码屏连接方式,COM端与段码屏的COM端对应连接,SEG端与段码屏的SEG端对应连接即可。

命令格式

HT1621包括两种模式,数据模式和命令模式,数据模式下有Read、Write、Read-Modify-Write,它们通过ID号进行区分。在命令模式下,一次数据格式有12位,高3位为ID位,后9位是其命令码,在数据模式下,一次数据格式有13位,高3位为ID位,6位的地址位,对应SEG端,4位的数据位,对应COM端。 alt text alt text

时序图

Write模式

alt text 从图中可以看出,当CS为低电平且WR在上升沿时才能写入数据。 根据这一点,我们可以写出发送一位数据到HT1621的函数。

/**
 * @brief 写一位数据到HT1621
 * @param data 数据
 * @param num 个数
 */
static void WriteBitToHT1621(uint8_t data, uint8_t num)
{
    for (uint8_t i = 0; i < num; i++)
    {
        LCD_WR_RESET(); // WR置低

        if (((data & 0x80) >> 7) == 1) // 如果当前bit为1,DATA置高
        {
            LCD_DATA_SET();
        }
        else if (((data & 0x80) >> 7) == 0) // 如果当前bit为0,DATA置低
        {
            LCD_DATA_RESET();
        }
        LCD_WR_SET(); // WR置高
        data <<= 1;   // 移位
    }
}

写入一位数据的函数写完之后,在Writ模式下,其数据格式为:3bit ID + 6bit Addr + 4bit Data,其函数实现如下:

#define WRITE_DATA_CODE 0xA0 // 发送数据
/**
 * @brief 发送数据到HT1621
 * @param addr 地址
 * @param dataVal 数据
 */
void WriteDataToHT1621(uint8_t addr, uint8_t dataVal)
{
    LCD_CS_RESET(); // CS置低
    WriteBitToHT1621(WRITE_DATA_CODE, 3);
    WriteBitToHT1621(addr << 2, 6);
    WriteBitToHT1621(dataVal << 4, 4);
    LCD_CS_SET(); // CS置高
}

alt text Write模式还支持连续写入模式,其数据格式为:3bit ID + 6bit Addr + Nbit Data,其函数实现如下:

/**
 * @brief 发送N个数据到HT1621
 * @param addr 地址
 * @param dataVal 数据
 * @param cnt 数据总数
 */
void WriteNDataToHT1621(uint8_t addr, uint8_t *dataVal, uint8_t cnt)
{
    LCD_CS_RESET(); // CS置低
    WriteBitToHT1621(WRITE_DATA_CODE, 3);
    WriteBitToHT1621(addr << 2, 6);
    for (uint8_t i = 0; i < cnt; i++)
    {
        WriteBitToHT1621(*dataVal++, 8);
    }
    LCD_CS_SET(); // CS置高
}

Command模式

在Command模式下,其数据格式为:3bit ID + 9bit Command,其函数实现如下:

#define WRITE_CMD_CODE 0x80  // 发送命令
/**
 * @brief 发送命令到HT1621
 * @param cmdVal 命令
 */
void WriteCmdToHT1621(uint8_t cmdVal)
{
    LCD_CS_RESET(); // CS置低
    WriteBitToHT1621(WRITE_CMD_CODE, 3);
    WriteBitToHT1621(cmdVal, 8);
    WriteBitToHT1621(0, 1);
    LCD_CS_SET(); // CS置高
}

段码屏显示实现

创建数组

创建一个16字节的数组用于保存128点位的段码屏数据。

/* LCD段码屏数据缓存 */
uint8_t array_RAM[16] = {
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00};

创建一个LCD扫描函数,通过定时器计时100ms刷新一次,完成屏幕显示内容更新。(100ms的时间可以根据需求自行修改)

/**
 * @brief 将缓存区的数据写入HT1621
 * @param
 */
void LcdScan(void)
{
    WriteNDataToHT1621(WRITE_DATA_CODE, 0, array_RAM, 16);
}

根据COM-SEG的对应关系和7段数码管显示原理,实现显示数字的数组。

/* 数码管数据表 */
const uint8_t array_num1[10] = {
    0xAF, 0xA0, 0xCB, 0xE9, 0xE4, // 0, 1, 2, 3, 4
    0x6D, 0x6F, 0xA8, 0xEF, 0xED  // 5, 6, 7, 8, 9
};

下面是1号数码管,2号数码管,3号数码管显示012的实现。

array_RAM[15] = (array_RAM[15] & ~0xEF) | array_num1[0]; // 1B 1G 1C T18 1A 1F 1E 1D
array_RAM[14] = (array_RAM[14] & ~0xEF) | array_num1[1]; // 2B 2G 2C T2 2A 2F 2E 2D
array_RAM[13] = (array_RAM[13] & ~0xEF) | array_num1[2]; // 3B 3G 3C T16 3A 3F 3E 3D

总结

段码屏的显示从原理到驱动实现,整体难度不大,主要是COM-SEG到RAM的映射关系,稍显繁琐。

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