C51: Splitting Code Between EPROM and Flash/EEPROM

Information in this article applies to:

• C51 All Versions

QUESTION

I'm using the Keil 8051 tools C and Assembly code for a project I'm designing. I need to create 2 separate code areas: one for code in EPROM and one for code in Flash or EEPROM.

The code in the EPROM will be fixed and will never change.

The code in the Flash/EEPROM will be downloaded from time to time to update the firmware.

The EPROM must call functions in the Flash/EEPROM but not vice-versa.

What's the best way to go about this?

ANSWER

There are a number of good ways to do this. The following method is only one suggestion.

1. You must create the BOOT program which resides at address 0000h. This program starts immediately after RESET.
2. You must create an EXTernal program which the BOOT program jumps to. The EXT program will probably start at 8000h or 4000h or something like that.
3. You must create a jump table in the BOOT program that the EXT program can use to access the BOOT's functions. You may also just use the fixed addresses of the BOOT's functions, but that's more difficult.
4. You must create BOOT's functions that will be called by EXT in such a way that they don't mess up EXT's variable space. The easiest way to do that is to use the small model reentrant stack.

The above "rules" were used in this bootloader example which you may download from the Keil web site.

Refer to the ABSTRACT.TXT file in the example for implementation details.

Last Reviewed: Thursday, February 25, 2021