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How to properly program one-time PROM or windowed EPROM MCUs?

Latest Updated:03/01/2005

Question:

(ROM)  Regarding programming one-time PROM or windowed EPROM MCUs:
(1) I'm using the Advantest PROM programmer R495A. When programming ROM, what device type setting should I use?
(2) When device type is set to 256, I see Mitsubishi M5M27C256 and M5M27C256A. What's the difference between the two?
(3) What happens if the MCU is programmed with the wrong device type? [2005/03/01]

Answer:

(1) Please use the type indicated in the instruction manual of the programming adapter you are using.

(2) The ROM type of M5M27C256 and M5M27C256A correspond to Renesas EPROM M5M27C256K and M5M27C256AK respectively. The difference in programming for the programmer is unclear, but EPROM access times differ.

(3) Even when programming with a type not listed in the instruction manual, if the programming operation is performed correctly by the programmer and verification is successful, that type can be considered to be nonproblematic.
We have tested and evaluated programming with on-chip ROM for each ROM setting found in our programming adapter instruction manuals. We neither recommend nor provide support for other ROM types which we have not evaluated.

Furthermore, we cannot make any predictions regarding the programmer control program, but the following general problems may be expected.
- If the speed margin is insufficient due to difference in EPROM access time, there will be a high risk of write defects (verification errors included).
- If "M5M27C256" is used for programs requiring "M5M27C101" or vice versa, miswrite errors will occur.
- Programmability of ROM types from other manufacturers is not guaranteed.
- When programming voltage other than that indicated in the instruction manual is used, the MCU or programming adapter may break if too much voltage is applied.

(#104889)

Suitable Products
3850A