C51: USING PDATA ON ADUC83X AND ADUC84X DEVICES

Information in this article applies to:

• C51 All Versions

SYMPTOM

PDATA is a 256-byte area of XDATA memory that is accessed using the MOVX @R0 and MOVX @R1 instructions.

On 8051 devices which externally address XDATA (XDATA is off-chip), the value of the P2 SFR is used as the upper address byte (R0 or R1 contain the lower address byte).

On devices with on-chip XDATA memory, P2 may be used for I/O and not as the upper address byte. Such cases require special settings for the PDATA configuration in the startup code and in the µVision Simulator.

RESOLUTION

The following lists how PDATA is accessed for certain devices:

• Analog Devices ADuc83x: When on-chip XRAM is enabled, PDATA is accessed as the first 256 bytes of XDATA space. PPAGE is 0.
• Analog Devices ADuc84x: When on-chip XRAM is enabled, PDATA is accessed as the first 256 bytes of XDATA space. PPAGE is 0.

MORE INFORMATION

• Refer to pdata in the Cx51 User's Guide.

SEE ALSO

• C51: USING PDATA MEMORY
• µVision DEBUGGER: SIMULATING PDATA MEMORY

Last Reviewed: Tuesday, October 24, 2006