MPC5604B/C Microcontroller Reference Manual, Rev. 8
74 Freescale Semiconductor
The communication is done in half duplex manner, whereby the transmission from the host is followed by
the microcontroller transmission mirroring the transmission back to the host:
• Host sends data to the microcontroller and waits for a response.
• MCU echoes to host the data received.
• Host verifies if echo is correct:
— If data is correct, the host can continue to send data.
— If data is not correct, the host stops transmission and the microcontroller enters static mode.
All multi-byte data structures are sent with MSB first.
A more detailed description of these steps follows.
5.2.1.3 Censorship mode detection and serial password validation
Before the serial download can commence, the BAM code must determine which censorship mode the
microcontroller is in and which password to use. It does this by reading the PUB and SEC fields in the
SSCM Status Register (see Section 5.3.4.1, System Status Register (SSCM_STATUS)) as shown in
Table 5-7.
When censorship is enabled, the flash memory cannot be read by application code running in the BAM or
in the SRAM. This means that the private password in the shadow flash memory cannot be read by the
BAM code. In this case the SSCM is used to obtain the private password from the flash memory of the
censored device. When the SSCM reads the private password it inverts the order of {NVPWD0,
NWPWD1} so the password entered over the serial download needs to be {NVPWD1, NVPWD0}.
Table 5-7. BAM censorship mode detection
SSCM_STATUS register fields
Mode Password comparison
PUB SEC
1 0 Uncensored, public password 0xFEED_FACE_CAFE_BEEF
0 0 Uncensored, private password NVPWD0,1 from flash memory via BAM
0 1 Censored, private password NVPWD1,0 from flash memory via SSCM
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