C51: Philips P8XC557E8 Internal AUX-RAM Support

Information in this article applies to:

• C51

QUESTION

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?

ANSWER

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

SEE ALSO

• C51: NXP/Philips 87C51RC 512-byte Internal RAM Support
• C51: Using Microcontrollers With On-chip XDATA

Last Reviewed: Thursday, February 25, 2021