Toshiba TLCS-870/C1 Series, Manual

Page: 369 / 408

Page 355
TMP89FM42
RA002
22.12Security
In serial PROM mode, two security functions are provided to prohibit illegal memory access attempts by a third
party: password and security program functions.
22.12.1Passwords
A password is one of the security functions, and can be used when the TMP89FM42 operates in serial
PROM mode or when the on-chip debugging function (hereafter called OCD) is used. Specifically, a password
can be established by using data (part of user memory) in flash memory. If a password is established, a pass-
word authentication process must be performed to execute the flash memory read command, flash memory
write command, and other operation commands. In the case of the OCD, the password authentication process is
required prior to the start of the OCD system.
In parallel PROM mode, there are no access-related restrictions using a password. To establish the access-
related restrictions that work in both serial and parallel PROM modes, the security program must be set to an
appropriate setting.
22.12.1.1How a password can be specified
With the TMP89FM42, any piece of data in flash memory (8 or more consecutive bytes) can be speci-
fied as a password. A password thus specified is authenticated by comparing a password string transmit-
ted by the external controller with the memory data string of MCU where the password is specified. The
area where a password can be specified is 0x8000 through 0xFEFF in flash memory.
22.12.1.2Password structure
A password consists of three components: PNSA, PCSA, and a password string. Figure 22-4 shows the
password structure (example of a transmitted password).
• PNSA (password count storage address)
A 3-byte address is specified in the area 0x8000 through 0xFEFF. The memory data of a
specified address is the number of bytes of a password string. If the memory data is less than
0x07 or if an address is outside the specified address range, a password error occurs.
The memory data specified here is defined as N.
• PCSA (password comparison start address)
A 3-byte address is specified in the area 0x8000 through 0xFEFF-N. An address thus speci-
fied is the starting address to be used to compare with a password string. If an address is outside
the specified address range, a password error occurs.
• Password string
Data of 8 bytes to 255 bytes (=N) must be specified as a password string. Memory data and a
password string are compared by a specified number "N" of bytes; a comparison starts at an
address specified by PCSA. If there is a mismatch as a result of this comparison or if data of 3
or more consecutive bytes is specified, a password error occurs, and the TMP89FM42 goes into
an idle state. In this idle state, external devices cannot communicate with the TMP89FM42. To
resume communication, the TMP89FM42 must be restarted in serial PROM mode by using the
reset pin.