MPC555
/
MPC556
CDR MoneT FLASH EEPROM
MOTOROLA
USER’S MANUAL
Rev. 15 October 2000
19-31
19.7.8 Controlling the Program/Erase Voltage
The external program or erase enable pin (EPEE) and EHV are used to control the ap-
plication of the program or erase voltage to the CMF EEPROM module. High voltage
operations to the CMF EEPROM array, special MoneT shadow locations or FLASH
NVM registers can occur only if EHV = 1 and EPEE = 1.
Only after the correct hardware and software interlocks have been applied to the CMF
EEPROM can EHV be set. Once EHV is set SES cannot be changed and attempts to
read the array will not be acknowledged.
The default reset state of EHV disables program or erase pulses (EHV = 0). A master
reset while EHV = 1 terminates the high voltage operation, and CMF generates the re-
quired sequence to disable the high voltage without damage to the high voltage cir-
cuits. A soft reset or disabling the internal memory map clears EHV, terminating the
high voltage pulse.
19.8 Censored and Non-Censored Accesses
The MPC555 / MPC556 always operates in one of two modes: censored or uncen-
sored.
19.8.1 Uncensored Mode
Uncensored mode provides no censorship. In uncensored mode the FIC, ACCESS,
and CENSOR[0:1] bits are irrelevant. The MPC555 / MPC556 operates in uncensored
mode unless a specific event occurs to place the device in censored mode.
19.8.2 Censored Mode
The MPC555 / MPC556 enters censored mode in response to any of the following
events:
• Booting from external memory
• Any CMF array access from an external master
• Entering background debug mode.
The CMF EEPROM censorship mechanism provides several censorship levels. Four
bits in CMFMCR are used to configure the CMF censorship level. These bits are listed
in
.
In censored mode, the ACCESS and CENSOR bits work together according to
Table 19-14 Censorship Control Bits
ACCESS
Enables a CMF EEPROM to bypass the censorship
FIC
Overrides CENSOR[0:1] to force information censorship if ACCESS = 0
CENSOR[0:1]
Determine the censorship level of the CMF
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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