I am trying to compile a C code using Keil uvision 3. The entire code gets compiled only if I use large memory model by choosing option xdata for target. To use this model I have to use external data RAM which is not possible for me due to some reasons.
So I decided to go with pdata option. Can anybody please help me with the exact steps to be carried out for using pdata? I am using 89V51RD2. I am much confused with the options like BL51 MISC, BL51 Locate etc.
You may have better luck posting this on the official Keil forum at
The NXP P89V51RD2 is an 8051 derivative with, according to the data sheet, 1KB of on-chip RAM. If your program will not fit in that much space, you will have to add external RAM.
PDATA lets you use "P"aged access to XDATA. It is not additional memory. If you need more space, you should really look at optimizing your memory usage, or you will have to add additional XDATA resources.
Reference: C51: USING PDATA MEMORY
Disclosure: I work for Keil/ARM
If you truly do not have any external data RAM available, then the PDATA option will not help you. PDATA resides in a different Logical address space from XDATA, but uses the same Physical Space.
For example, the micro-controller that you're using contains 1kB of RAM. All 1024 bytes can be accessed as XDATA memory (Addresses XDATA:0x0000 to XDATA:0x03FF). 256 bytes (at a time) can be accessed as PDATA memory (Addresses PDATA:0x00 to PDATA:0xFF). Let's assume that you set up the micro-controller to use the first 256 bytes of RAM as PDATA memory. That means that PDATA:0x00 and XDATA:0x0000 point to the same physical byte of RAM. If you're not careful, you will try to store two different values in the same physical piece of memory and one of them will be overwritten and lost.
If you are already using all of your XDATA memory, you will need to use the DATA memory or the IDATA memory to get more. If you do use IDATA memory, you will need to be very careful that you leave enough space empty so that the values you are storing aren't accidentally overwritten by the stack which starts at IDATA:0xFF and grows down towards IDATA:0x00
Edit: Sorry, I didn't notice that this question was two years old. Hopefully this helps someone, though.
