PDATA and XDATA

Jerry;
I second your choice of an ARM eval kit. But I would like to address a concern already expressed in previous replies to your post.

Selecting Compact does not speed up the overall access of external memory. It will speed up some access to external memory within the page size of PDATA.

Selecting Compact allows the Compilier/Linker to assign vars to the PDATA area but if you move the PDATA area beyond the first 256 bytes of external memory then you must handle the high address lines of P2.

But I will be adding a few things to it and I just want some peace of mind. (Your Post).

If you add many vars, you will be treading on your stack quickly. Remember, by selecting the Compact model, you are telling Keil Tools to put all your vars in PDATA.

By selecting the Small Memeory model and explicitly assigning your stack variables to PDATA will, IMHO, result in a little more secure and faster external memory access over all.

In this manner, your auto vars will be assigned to the DATA memory and your explicitly assigned vars will go to the PDATA area.

In my years of 8051, I have found the PDATA area only useful for quickly accessing memory mapped I/O where I was controlling P2 for the high address decoding.

Talking with a number of Keil people at the trade shows, they wished they had never implemented PDATA but it was previously defined by INTEL so they had clients ask "where is my PDATA?".

All in all, I agree with Andy. If you need to build a pseudo stack you should be using a different MCU.
Bradford

Jerry;
I second your choice of an ARM eval kit. But I would like to address a concern already expressed in previous replies to your post.

Selecting Compact does not speed up the overall access of external memory. It will speed up some access to external memory within the page size of PDATA.

Selecting Compact allows the Compilier/Linker to assign vars to the PDATA area but if you move the PDATA area beyond the first 256 bytes of external memory then you must handle the high address lines of P2.

But I will be adding a few things to it and I just want some peace of mind. (Your Post).

If you add many vars, you will be treading on your stack quickly. Remember, by selecting the Compact model, you are telling Keil Tools to put all your vars in PDATA.

By selecting the Small Memeory model and explicitly assigning your stack variables to PDATA will, IMHO, result in a little more secure and faster external memory access over all.

In this manner, your auto vars will be assigned to the DATA memory and your explicitly assigned vars will go to the PDATA area.

In my years of 8051, I have found the PDATA area only useful for quickly accessing memory mapped I/O where I was controlling P2 for the high address decoding.

Talking with a number of Keil people at the trade shows, they wished they had never implemented PDATA but it was previously defined by INTEL so they had clients ask "where is my PDATA?".

All in all, I agree with Andy. If you need to build a pseudo stack you should be using a different MCU.
Bradford

Thanks Al,

I understand at little more know. If I do have problem I will just redefine it. Moving everything back to standard stack and if I need PDATA just assigning it. I did do some benchmarks and when I made the change to PDATA it did show some and improvement. But my orignal question has not really been asnwered. e.g.

PDATA char data[255];
XDATA char data2[255];

Do these two array go to the same memory location?

I think not - but can't be sure.

Similarly, I think, IDATA and DATA don't overlap (as far as C51 is concerned).

You should be able to see this from the Map file?

Map File? I am no genius on keil, is there a map file?

aka "Linker Listing file"

Is this possible to transmit data in decimal through serial port because according to my knowledge serial port can transmits only ASCII characters but it can receive decimal/binary data if there is any method to transmit decimal/binary data using it please reply

Regards

Kingky

PDATA and XDATA

on new subject styart a new thread

Erik

you may notice that ASCII characters include 0x00 to 0xFF, not only visible characters.
so you can send any 8bit data use "send char" or simlar fuction, but don't use "send string", beacause string is 0x00 as end.

in many application, for easy(clearly) view the data in terminal, add a 0x30 for BCD number