National CP3BT26 - Manual (Page 34)

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CP3BT26
8.4 INFORMATION BLOCK WORDS
Two words in the information blocks are dedicated to hold
settings that affect the operation of the system: the Function
Word in Information Block 0 and the Protection Word in In-
formation Block 1.
8.4.1 Function Word
The Function Word resides in the Information Block 0 at ad-
dress 07Eh. At reset, the Function Word is copied into the
FMAR0 register.
USB_ENABLE The USB_ENABLE bit can be used to force
an external USB transceiver into its low-power
mode. The power mode is dependent on the
USB controller status, the USB_ENABLE bit
in the MCFG register (see Section 7.1), and
the USB_ENABLE bit in the Function Word.
0
– External USB transceiver forced into low-
power mode.
1 – Transceiver power mode dependent on
USB controller status and programming
of the Function Word.
8.4.2 Protection Word
The Protection Word resides in Information Block 1 at ad-
dress 0FEh. At reset, the Protection Word is copied into the
FMAR1 register.
BOOTAREA The BOOTAREA field specifies the size of the
Boot Area. The Boot Area starts at address 0
and ends at the address specified by this field.
The inverted bits of the BOOTAREA field
count the number of 2048-byte blocks to be
reserved as the Boot Area. The maximum
Boot Area size is 30K bytes (address range 0
to 77FFh). The end of the Boot Area defines
the start of the Code Area. If the device starts
in ISP mode and there is no Boot Area defined
(encoding 1111b), the device is kept in reset.
Table 14 lists all possible boot area encod-
ings.
EMPTY The EMPTY field indicates whether the flash
program memory has been programmed or
should be treated as blank. If a majority of the
three EMPTY bits are clear, the flash program
memory is treated as programmed. If a major-
ity of the EMPTY bits are set, the flash pro-
gram memory is treated as empty. If the
ENV[1:0] inputs (see Section 6.1) are sam-
pled high at reset and the EMPTY bits indicate
the flash program memory is empty, the de-
vice will begin execution in ISP mode. The de-
vice enters ISP mode without regard to the
EMPTY status if ENV0 is driven low and
ENV1 is driven high.
ISPE The ISPE field indicates whether the Boot
Area is used to hold In-System-Programming
routines or user application routines. If a ma-
jority of the three ISPE bits are set, the Boot
Area is intended to store ISP routines. If ma-
jority of the ISPE bits are clear, the Boot Area
holds user application routines. Table 15 sum-
marizes all possible EMPTY, ISPE, and Boot
Area settings and the corresponding start-up
operation for each combination. In DEV
mode, the EMPTY bit settings are ignored and
the CPU always starts executing from address
0.
15 1 0
Reserved USB_ENABLE
15 13 12 10 9 7 6 4 3 1 0
WRPROT RDPROT ISPE EMPTY BOOTAREA
Table 14 Boot Area Encodings
BOOT
AREA Size of the Boot
Area
Code Area
Start
Address
1111 No Boot Area defined 00 0000h
1110 2K bytes 00 0800h
1101 4K bytes 00 1000h
1100 6K bytes 00 1800h
1011 8K bytes 00 2000h
1010 10K bytes 00 2800h
1001 12K bytes 00 3000h
1000 14K bytes 00 3800h
0111 16K bytes 00 4000h
0110 18K bytes 00 4800h
0101 20K bytes 00 5000h
0100 22K bytes 00 5800h
0011 24K bytes 00 6000h
0010 26K bytes 00 6800h
0001 28K bytes 00 7000h
0000 30K bytes 00 7800h