说明：  编写将单片机片内一组RAM单元清0的函数，函数内不包括这组RAM单元的起始地址和单元个数，起始地址和单元个数参数应在执行函数前由主函数赋值。
(Write a function that clears a group of RAM units in a single chip. The function does not include the starting address and the number of units. The starting address and the number of units should be assigned by the main function before the function is executed.)