National CP3BT26 manual Module Status Register Mstat, Software Reset Register Swreset

CP3BT26

7.2MODULE STATUS REGISTER (MSTAT)

The MSTAT register is a byte-wide, read-only register that indicates the general status of the device. The MCFG regis- ter format is shown below.

7		6	5		4			3	2	0
ISPRST	WDRST			Res.		DPGMBUSY	PGMBUSY		OENV2:0
OENV2:0		The Operating Environment bits hold the
		states sampled from the ENV[2:0] input pins
		at reset. These states are controlled by exter-
		nal hardware at reset and are held constant in
		the register until the next reset.
PGMBUSY		The Flash Programming Busy bit is automati-
		cally set when either the program memory or
		the data memory is being programmed or
		erased. It is clear when neither of the memo-
		ries is busy. When this bit is set, software must
		not attempt to program or erase either of
		these two memories. This bit is a copy of the
		FMBUSY bit in the FMSTAT register.
		0 – Flash memory is not busy.
		1 – Flash memory is busy.
DPGMBUSY		The Data Flash Programming Busy indicates
		that the flash data memory is being erased or
		a pipelined programming sequence is current-
		ly ongoing. Software must not attempt to per-
		form any write access to the flash program
		memory at this time, without also polling the
		FSMSTAT.FMFULL bit in the flash memory in-
		terface. The DPGMBUSY bit is a copy of the
		FMBUSY bit in the FSMSTAT register.
		0 – Flash data memory is not busy.
		1 – Flash data memory is busy.
WDRST		The Watchdog Reset bit indicates that a
		Watchdog timer reset has occurred. Write a 1
		to this bit to clear it. Power-on reset also
		clears this bit.
		0 – No Watchdog timer reset has occurred
			since this bit was last cleared.
		1 – A Watchdog timer reset has occurred
			since this bit was last cleared.
ISPRST		The Software ISP Reset bit indicates that a
		software ISP reset has occurred since the bit
		was		last	cleared. This bit			is cleared		by a

SWRESET(CLR) sequence or a power-on re- set.

0 – No software ISP reset has occurred since this bit was last cleared.

1 – A software ISP reset has occurred since this bit was last cleared.

7.3SOFTWARE RESET REGISTER (SWRESET)

The SWRESET register is a byte-wide, write-only register which provides a mechanism for software to initiate a reset into ISP mode without regard to the status of the EMPTY bits in the flash protection word. This form of reset is only al- lowed when all of the following conditions are true:

„The device is in IRE or ERE mode

„BOOTAREA is defined (has a value other than 1111b) in the Protection Word (see Section 8.4.2 for more details).

„ISPE is set in the flash protection word, indicating that there is ISP code in the flash

To initiate a reset under these conditions, it is necessary to write the value E1h to the SWRESET register, followed with- in 127 clock cycles by the value 3Eh. The reset then follows immediately. This sequence is called SWRESET(ISP).

Once the device has been reset into ISP mode by SWRE- SET(ISP), any subsequent reset (other than internal or ex- ternal power-on reset) will cause the part to reset into ISP mode because the EMPTY bits in the Protection Word con- tinue to be ignored.

A second set of special values written to the SWRESET reg- ister will cause a reset out of ISP mode (whether or not the device is currently in ISP mode). This can be used as a sim- ple software reset. In this case, no conditions are checked. To initiate reset out of ISP mode, write the value E1h to the SWRESET register, followed within 127 clock cycles by the value 0Eh. The reset then follows immediately. This se- quence is called SWRESET(CLR). This reset also cancels the effect of any previous SWRESET(ISP), so subsequent resets will check the EMPTY bits to determine whether to enter ISP mode.

The ISP reset behaves similarly to the Watchdog reset, for example, if the flash interface is busy when reset is assert- ed, the reset to the clock module is delayed until the flash operations are completed.

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