National CP3BT26 manual Information Block Words, Boot, Area

CP3BT26

8.4INFORMATION 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.

8.4.1Function 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.

15	1	0
Reserved		USB_ENABLE

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.

8.4.2Protection Word

The Protection Word resides in Information Block 1 at ad- dress 0FEh. At reset, the Protection Word is copied into the FMAR1 register.

15	13	12	10	9	7	6	4	3	1	0
WRPROT		RDPROT		ISPE		EMPTY		BOOTAREA

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.

	Table 14 Boot Area Encodings
	BOOT	Size of the Boot	Code Area
			Start
	AREA	Area
			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
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.

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