怎么将I2C RTC和EEPROM与18F420接口

我正在尝试将I2C RTC（MCP7940N）和EEPROM（24LC32 A）与18F420接口。我以前在18F45 2上做了一个实验室（是的，我知道它已经过时了，它是我必须学习的DEV板Labx1），在其中我为同一EEPROM写了I2C函数，它运行在4MHz。我把代码移植到在20MHz XTAL上运行在18F420上的我的项目上。我改变了SSPADAD= 0x31；具体来说，我要做的是读取RTC芯片上的寄存器。代码执行；直到SSPCON2BIT.RCEN＝1；//启用接收同时（！）SSPSTATbits.BF），它挂在时间，显然表明，SSPBUF从来没有填补。我为EEPROM和RTC写了单独的读写功能，因为EEPROM的内部存储器从0x00到0x0FFF，而RTC只有一个字节的存储器地址从0x00到0x60，所以我必须写两个地址从EEPROM和一个RTC。我认为这可能是一个问题的函数，所以我试着从EEPROM读取它是挂在同一点，SSPSTATbits.BF总是停留在0。我选择了一个非法的XTAL值吗？我是否将SSPADD设置为正确的值？它在数据表中说，在SSPCON2BITS RCEN＝1之前，I2C必须是空闲的，但我认为我正在这样做…它似乎是写作，因为否则它会挂在等待ACK，对不对？我错过了什么？我的I2C函数位于代码的最底层…



      以下为原文

    I am trying to interface an I2C RTC (MCP7940N) and EEPROM (24LC32a) with the 18F4520. I had previously done a lab on the 18F452 (yes I know it's terribly obsolete, it's the dev board LabX1 I had to learn on) in which I wrote I2C functions for the same EEPROM and it worked running at 4MHz. I ported the code over to my project running on the 18F4520 on a 20MHz Xtal. I changed the SSPADD=0x31;

Specifically, what I'm trying to do is read the registers on the RTC chip. The code executes until;
SSPCON2bits.RCEN=1; // enable receive
while( !SSPSTATbits.BF );

It hangs on the while, apparently indicating that the SSPBUF is never filling. I wrote separate read and write functions for the EEPROM and the RTC because the internal memory of the EEPROM goes from 0x0000 to 0x0FFF while the RTC only has one byte of memory addresses from 0x00 to 0x60, so I have to write two addresses from the EEPROM and one for the RTC. I thought it might be a problem with the function, so I tried reading from the EEPROM and it is hanging at the exact same point, SSPSTATbits.BF is always stuck on 0.

Did I pick an illegal Xtal value? Did I set the SSPADD to a correct value? It says in the datasheet that i2c must be idle before SSPCON2bits.RCEN = 1, but I think I am doing that... It seems to be writing because otherwise it would hang waiting for the ACK, right? What am I missing? My i2c functions are at the very bottom of the code...


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