ARM Technical Support Knowledge Articles


Applies to: C51 C Compiler


Information in this article applies to:


The Philips P8xC557E8 8051 microcontroller features 2Kb of internal RAM. This is divided up into 128 bytes of data, 128 bytes of idata and 1792 bytes of AUX-RAM. Can I use the AUX-RAM in my programs? If so, how do I access it?


Yes, you can use the AUX-RAM in one of these devices. The RAM can either be used as one page of PDATA memory (totalling 256 bytes) or 1792 bytes of XDATA memory.

If you are using the AUX-RAM as XDATA, then make sure you set ARD to 0 to enable the AUX-RAM, and define your variables as XDATA.

If you are using the AUX-RAM as PDATA, then make sure you set ARD to 0 and XRAMP to a constant value. Define your variables as PDATA. Currently only one page of PDATA is supported. It is not possible to locate variables in more than one page of PDATA, so selecting another page by changing XRAMP is pointless and will cause your variables to "disappear".

Setting ARD to 1 accesses external RAM whenever variables in xdata or pdata are used.


Article last edited on: 2006-10-24 13:40:09

Rate this article

Disagree? Move your mouse over the bar and click

Did you find this article helpful? Yes No

How can we improve this article?

Link to this article
Copyright © 2011 ARM Limited. All rights reserved. External (Open), Non-Confidential