hexdump that requires only a putchar() function, for microcontoller

hexdump.c

void hexDump(char *description, void *basisAddr, void *startAddr, unsigned long len) {
   unsigned char i = 0;
   unsigned long tempAdr;
   char hex[] = "0123456789abcdef";
   unsigned char buff[17], *ptrBuf;
   unsigned char *pc = (unsigned char*) startAddr;
   if (description != NULL) {
       while (*description)
           putchar(*description++);
       putchar('\n');
   }
   while (len--) {
       if (i >= 16) {
           i = 0;
           putchar(' ');
           putchar(' ');
           ptrBuf = buff;
           while (*ptrBuf)
               putchar(*ptrBuf++);
           putchar('\n');
       }
       if (i == 0) {
           putchar(' ');
           putchar(' ');
           tempAdr = pc - (unsigned char*) basisAddr;
           putchar(hex[(tempAdr >> 28) & 0xf]);
           putchar(hex[(tempAdr >> 24) & 0xf]);
           putchar(hex[(tempAdr >> 20) & 0xf]);
           putchar(hex[(tempAdr >> 16) & 0xf]);
           putchar(hex[(tempAdr >> 12) & 0xf]);
           putchar(hex[(tempAdr >>  8) & 0xf]);
           putchar(hex[(tempAdr >>  4) & 0xf]);
           putchar(hex[tempAdr & 0xf]);
           putchar(' ');
       }
       putchar(' ');
       putchar(hex[(*pc >>  4) & 0xf]);
       putchar(hex[*pc & 0xf]);
       if ((*pc < 0x20) || (*pc > 0x7e))
           buff[i] = '.';
       else
           buff[i] =  *pc;
       buff[i + 1] = '\0';
       pc++;
       i++;
   }
   while (i++ < 16) {
       putchar(' ');
       putchar(' ');
       putchar(' ');
   }
   putchar(' ');
   putchar(' ');
   ptrBuf = buff;
   while (*ptrBuf)
       putchar(*ptrBuf++);
   putchar('\n');
}

Thanks! But what is the basisAddr? What value to use for basisAddr? NULL?
Usually hexdump is defined as: void hexdump(void *mem, unsigned int len).

startAddr is like mem
with basisAddr, you decide if you want the memory address to absolute if basisAddr = 0, or relative then you can change basisAddr = mem.

Thanks! I use NULL then.