Register Descriptions
set the bit, while writing a 1 to the bit will clear it.
6.5.2.4 External Reset (EXTR)—Bit 3
If 1, the EXTR bit indicates an external system reset has occurred. This bit will be cleared by a Power-On
Reset or by software. Writing a 0 to this bit position will set the bit, while writing a 1 to the bit position
will clear it. Basically, when the EXTR bit is 1, the previous system reset was caused by the external
RESET pin being asserted low.
6.5.2.5
Power-On Reset (POR)—Bit 2
When 1, the POR bit indicates a Power-On Reset occurred some time in the past. This bit can be cleared
only by software or by another type of reset. Writing a 0 to this bit will set the bit, while writing a 1 to the
bit position will clear the bit. In summary, if the bit is 1, the previous system reset was due to a Power-On
Reset.
6.5.2.6
Reserved—Bits 1–0
This bit field is reserved or not implemented. It is read as 0 and cannot be modified by writing.
6.5.3
SIM Software Control Registers (SIM_SCR0, SIM_SCR1, SIM_SCR2,
and SIM_SCR3)
Only SIM_SCR0 is shown in this section. SIM_SCR1, SIM_SCR2, and SIM_SCR3 are identical in
functionality.
Base + $2
15
14
13
12
11
10
9
8
7
6
5
4
3
2
0
1
0
0
0
Read
Write
POR
FIELD
0
0
0
0
0
0
0
0
0
0
0
0
0
Figure 6-5 SIM Software Control Register 0 (SIM_SCR0)
Software Control Data 1 (FIELD)—Bits 15–0
6.5.3.1
This register is reset only by the Power-On Reset (POR). It has no part-specific functionality and is
intended for use by a software developer to contain data that will be unaffected by the other reset sources
(RESET pin, software reset, and COP reset).
6.5.4
Most Significant Half of JTAG ID (SIM_MSH_ID)
This read-only register displays the most significant half of the JTAG ID for the chip. This register reads
$11F4.
56F8345 Technical Data, Rev. 17
Freescale Semiconductor
Preliminary
109
FREESCALE [ Freescale ]
