When we try to Break WINBOND MCU W78E516 Eeprom Memory, there is an issue which is unable to avoid which is called EMI emission, and engineer need to figure out the way to reduce this Electro-magnetic emission interference. below we are going to introduce the cause of this interference and the way to reduce it:
Because of on-chip Flash EPROM, when a program is running in internal ROM space, the ALE will be unused. The transition of ALE will cause noise, so it can be turned off to reduce the EMI emission if it is useless. Turning off the ALE signal transition only requires setting the bit 0 of the AUXR SFR, which is located at 08Eh.
When ALE is turned off, it will be reactivated when the program accesses external ROM/RAM data or jumps to execute an external ROM code. The ALE signal will turn off again after it has been completely accessed or the program returns to internal ROM code space. The AO bit in the AUXR register, when set, disables the ALE output.
In order to reduce EMI emission from oscillation circuitry, W78E51B allows user to diminish the gain of on-chip oscillator amplifiers by using programmer to clear the B7 bit of security register. Once B7 is set to 0, a half of gain will be decreased after Break WINBOND MCU W78E516 Eeprom Memory.
Care must be taken if user attempts to diminish the gain of oscillator amplifier, reducing a half of gain may effect to external crystal operating improperly at high frequency above 24 MHz. The value of R and C1, C2 may need adjustment while running at lower gain before BREAK IC.