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MARC4 4-bit Microcontrollers Errata Sheet

4813A–4BMCU–06/04

Workaround

MTP Parts

a) Experienced customers using Atmel MTP parts (ATAM893S, ATAM894P) can modify the

HEX-file directly. Within each interrupt service routine, replace the HEX-code for CCR! in front

of the RTI with a SCALL to a free address. Introduce the HEX-codes for the commands LIT_1,

OR, CCR! and EXIT at this address. Now, with each RTI, the interrupt enable flag is set. This

software modification overrides the last hardware modification, i.e., the parts behave as if not

having received DI-enhancement, and the interrupt active register will be cleared correctly.

b1) An equivalent modification can be done in the source code, but the modification depends

on the content the compiler saved at the beginning of an interrupt service routine:

0080

: INT1

0080 0D

CCR@

\$SAVEREG

0081 73

Y@

0082 72

X@

In this case, CCR, X and Y registers were saved, therefore, the modification should look as

follows:

2>R 2>R 1 or 2R> 2R>

either at the beginning or at the end of the interrupt service routine.

b2) If only CCR and one of the registers were saved:

01E0

:INT7

01E0 0D

CCR@

\$SAVEREG

01E1 73

Y@

The modification looks as follows:

ROT 1 or <ROT

c) Customers using MTP parts may switch their order to the predecessor version.

ROM Parts

Customers using ROM parts may switch their order to the predecessor version.

Up to now it has not occurred, that parts working correctly under all conditions might fail in the

future or under different environmental conditions.