Lucent Technologies MN10285K User Manual

288

The ROM correction function can correct the program data in any address within 

the 256-kilobyte ROM. (It cannot correct OSD ROM data.) A maximum of 
sixteen addresses can be corrected. Addresses are set as address match interrupts. 

This function shortens time-to-market for large-scale designs, since changes can 
be implemented in the software after the mask ROM is complete.

The ROM correction function has numerous other applications. For instance, you 
can insert keywords into the functional routines, then use the function to send 

internal status information to an external location. This enables system-level 
examination of the internal status even with the mask ROM version.

To use the ROM correction function, embed a routine such as that shown in 
figure 12-2 in the ROM.

As figure 12-1 shows, the function lies between the microcontroller and ROM 
blocks. First set the correction data for any sixteen non-OSD addresses in the 

ROM correction address match and data registers. (Follow the flow shown in 
figure 12-2.) Once this is done, the circuit will correct the ROM output for the 

designated addresses.

ROM

address

CPU

ROM

correction

Instruction
counter

Instruction
fetch

ROM

Start

Is ROM

correction

required?

Set up the

correction data

Enable the

correction function

Main

Necessary
software settings

Yes

No