C51: MEMORY TYPES FOR THE DALLAS 390 CONTIGUOUS MODE

Information in this article applies to:

• C51 Version 6.23

QUESTION

I'm using the Dallas 390 in contiguous mode. When referring to the Cx51 User's Guide 02.2002, I find the explanation for the format of Generic and Far pointers used with Classic 8051 and Philips 80C51MX devices but not for the Dallas 390 in contiguous mode.

I need to understand the memory types for the 390. What is the exact format?

ANSWER

As you know, generic pointers require 3 bytes (24 bits). The first byte is the Memory Type Byte. The following two bytes are the MSB and LSB of the offset. The Memory Type Byte values are defined in the following table.

Memory Type Byte   Addressed Memory Region
------------------------------------------
0x00               DATA/IDATA/BDATA
0x01-0x7F          XDATA memory -- X:0x00:0000-X:0x7E:FFFF
0x80               Unused
0x81-0xFF          CODE memory  -- C:0x00:0000-C:0x7E:FFFF

Note that 8MB minus 64KB is supported for XDATA and for CODE.

In C51 Version 6.23, the Run-Time Library was revised to provide better support for the Dallas 390 contiguous mode. The performance of Generic and Far pointers has improved considerably.

MORE INFORMATION

• Refer to far in the Cx51 User's Guide.
• Refer to Data Storage Formats in the Cx51 User's Guide.
• Refer to Absolute Memory Locations in the Cx51 User's Guide.
• Refer to Absolute Access Macros in the Cx51 User's Guide.
• Refer to The _at_ Keyword in the Cx51 User's Guide.

SEE ALSO

• C51: CONFIGURING FOR THE DALLAS 390 CONTIGUOUS MODE
• C51: ABSOLUTE ACCESS FOR FAR VARIABLES
• C51: ABSOLUTE MEMORY ACCESSES TO DALLAS 390'S FAR MEMORY

FORUM THREADS

The following Discussion Forum threads may provide information related to this topic.

• function pointers in Dallas 390 contiguous mode
• overwriting ds80c400 interrupt vectors

Last Reviewed: Friday, July 15, 2005