Dear Sirs,

We are requesting further information on a particular problem we recently experienced with the following µP: AT89C205112PC. Our R&D dept is not able to solve this quite surprising phenomenon.

Please find here below the transcript of our problem.

1. We have downloaded a specific and identical program to a 10 units series of the AT89C205112PC µP from the same lot.
2. This processor has been given a master role on a circuit.
3. We have tested the speed of each unit with the very same environment i.e. Board, alimentation, temperature, humidity, program and language.
4. We have determined that the timing of the execution of the program is split into 4 mains groups.
5. Group 1 can achieve the task in less than 5'sec.(1 unit), Group 2 in 16'sec.(8 units), Group 3 in 32'sec.(1 units), Group 4 in 40'sec.(1 units). There is no particular raison for this phenomenon.
6. We have renewed this experience after implementing the µprocessor one after the others on a new board.
7. The results were identical.
8. We have uploaded the program contained in the group 1 µprocessor to a PC and downloaded again to another µprocessor.
9. As a result the speed of execution is 16'sec.

We suspect that the AT89C205112PC contains a unknown factor probably a pull up "resistor" or "impedance" variation that peace the execution of the program.
Firstly, we would like to understand or identify the origin of these timing differences.
Secondly, we would like you to confirm or denied the pull up resistor thesis.
Thirdly, we would appreciate to control this speed factor.

If you need any further information on this topic, please, feel free to contact with us.

Best regards,