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Chapter 53 Fixed Mode-Reset Vector / BOOT-ROM
1.Overview
Chapter 53 Fixed Mode-Reset Vector / BOOT-ROM
1. Overview
The Boot ROM is a fixed start-up routine, which is located at memory addresses 0xB000 to 0xBFFF. The entry
point 0xBFF8 is determined by the Fixed Reset Vector if the device is configured with the mode pins set to
MD[2:0]=”000” (internal ROM/vector mode). In this mode MB91460 series devices use the Fixed Mode Vector data
(FMV, address 0x0F:FFF8, data 0x06000000) and Fixed Reset Vector data (FRV, address 0x0F:FFFC, data
0x0000BFF8). The data of both these vectors are independent from the flash content at these two addresses.
The purpose of the Boot ROM is to configure the device after a reset and to provide a simple serial bootloader for
programming the embedded flash memories.
Therefore it is executed always after the Reset Cancellation Sequence (see chapter 5.6 Reset Cancellation
Sequence (Page No.147) or 7.6 Reset Cancellation Sequence (Page No.149)) of every INIT or RST reset.
2. Check for Boot Conditions
The check for boot conditions is slightly different for the evaluation chip MB91V460 (A-version) and the flash
derivates (e.g. MB91F467DA).
2.1 Evaluation Chip MB91V460
After the chip initialization and saving the RSRR (Reset Cause Register) to CPU register R4, the Boot Security
Vector (BSV: Vector #144, 0x0F:FDBC) will be checked. This check is performed as follows: if the data of this
vector represents a valid address in the specified address range, the Boot Security Vector itself becomes valid.
If the Boot Security Vector is valid, the Boot ROM is left and the user application is started at the address given by
this vector.
The purpose of this feature is to disable the execution of the internal bootloader due to security reasons or to
minimize startup time of the application. Only if the user sets the Boot Security Vector to an address outside the
given address range or leaves this vector at default content after erase (0xFFFF:FFFF) the internal bootloader can
be entered.
If the Boot Security Vector is not valid, the reset cause will be checked as second boot condition. Only if the reset
cause was an INIT reset (external INITX pin input, RSRR=0x80), the check for boot conditions will go on.
Otherwise Boot ROM is left and application is started at default user program entry address 0x0F:4000.
If the reset cause was an INIT reset, UART0 is initialized: 2400 baud, 8 data bits, 1 stop bit, no parity. UART-
reception is checked for about 100 ms. If during this time period the ASCII-character “V” (0x56) is received, the
internal bootloader is entered. Otherwise Boot ROM is left and application is started at default user program entry
address 0x0F:4000.
Device Valid Boot Security Vector address range
MB91V460 0x04:0000 – 0x13:FFFF