MIC3000BML datasheet(32/68 Pages) MICREL

32 / 68 page

MIC3000

Micrel

M9999-101204

October 2004

Acknowledge Polling

The MIC3000’s non-volatile memory cannot be accessed

during the internal write process. To allow for maximum

speed bulk writes, the MIC3000 supports acknowledge poll-

ing. The MIC3000 will not acknowledge serial bus transac-

tions while internal writes are in progress. The host may

therefore monitor for the end of the write process by periodi-

cally checking for an acknowledgement.

Write Protection and Data Security

OEM Password

A password is required to access the OEM areas of the

MIC3000, specifically the non-volatile memory, look-up tables,

and registers at serial addresses A4h and A6h. A four-byte

field, OEMPWSET, at serial address A6h is used for setting

the OEM password. The OEM password is set by writing

OEMPWSET with the new value. The password comparison

is performed following the write to the MSB of the OEMPW,

address 7Bh at serial address A2h. Therefore, this byte

must be written last! A four-byte burst-write sequence to

address 78h may be used as this will result in the MSB being

written last. The new password will not take effect until after

a power-on reset occurs or a warm reset is performed using

the RST bit in OEMCFG0. This allows the new password to

be verified before it takes effect.

The corresponding four-byte field for password entry, OEMPW,

is located at serial address A2h. This field is therefore always

visible to the host system. OEMPW is compared to the four-

byte OEMPWSET field at serial address A6h. If the two fields

match, access is allowed to the OEM areas of the MIC3000

non-volatile memory at serial addresses A4h and A6h. If

OEMPWSET is all zeroes, no password security will exist.

The value in OEMPW will be ignored. This helps prevent a

deliberately unsecured MIC3000 from being inadvertently

locked. Once a valid password is entered, the MIC3000 OEM

areas will be accessible. The OEM areas may be re-secured

D7 D6 D5 D4 D3 D2 D1 D0 A

D3 D2 D1 D0

/A P

3rd Data Byte to

MIC3000

4th Data Byte to

MIC3000

STOP

R/W = READ

ACKNOWLEDGE

NOT ACKNOWLEDGE

Master to slave transfer,

i.e., DATA driven by master.

Slave to master transfer,

i.e., DATA driven by slave.

• • •

S 1010

000

0 AXXXXXXXXA

MIC3000 Slave Address

DATA

CLK

START

R/W = WRITE

ACKNOWLEDGE

D7 D6 D5 D4 D3 D2 D1 D0 A

D2 D1 D0

1st Data Byte to

MIC3000

2nd Data Byte to

MIC3000

ACKNOWLEDGE

Figure 24. Four-Byte Page_Write Protocol

by writing an incorrect password value at OEMPW, e.g., all

zeroes. In all cases OEMPW must be written LSB first

through MSB last. The OEM areas will be inaccessible

following the final write operation to OEMPW’s LSB. The

OEMPW field is reset to all zeros at power on. Any values

written to these locations will be readable by the host regard-

less of the locked/unlocked status of the device. If OEMPWSET

is set to zero (00000000h), the MIC3000 will remain unlocked

regardless of the contents of the OEMPW field. This is the

factory default security setting.

NOTE: A valid OEM password allows access to the OEM and

user areas of the chip, i.e., the entire memory map, regard-

less of any user password that may be in place. Once the

OEM areas are locked, the user password can provide

access and write protection for the user areas.

User Password

A password is required to access the USER areas of the

MIC3000, specifically the non-volatile memory at serial ad-

dresses A0h and A2h. A one-byte field, USRPWSET at serial

address A2h is used for setting the USER password.

USRPWSET is compared to the USRPW field at serial

address A2h. If the two fields match, access is allowed to the

USER areas of the MIC3000 non-volatile memory at serial

addresses A0h and A2h.The USER password is set by writing

USRPWSET with the new value. The new password will not

take effect until after a power-on reset occurs or a warm reset

is performed using the RST bit in OEMCFG0. This allows the

new password to be verified before it takes effect.

NOTE: A valid OEM password allows access to the OEM and

user areas of the chip, i.e., the entire memory map, regard-

less of any user password that may be in place. Once the

OEM areas are locked, the user password can provide

access and write protection for the user areas. If a valid OEM

password is in place, the user password will have no effect.

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