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Register Descriptions (SYS_BASE = $1FFF08)
System Integration Module (SIM), Rev. 4
Freescale Semiconductor
4-9
4.6 Register Descriptions (SYS_BASE = $1FFF08)
4.6.1 SIM Control Register (SCR)
Figure 4-3. SIM Control Register (SCR)
See Programmer’s Sheet on Appendix page B-8
4.6.1.1 Reserved—Bit 15
This bit is reserved or not implemented. It is read as 0, but it cannot be modified by writing.
4.6.1.2 Boot Mode—Bits 14–12
These boot mode bits replace the mode bits in the 56800E OMR.
This field is set to the value on the input pins, MODA, MODB, and MODC, when the last active
reset source—reset pin, power-on reset—deasserts. Synchronous reset (software or COP) do not
update Boot mode assuming applications software will set the desired field value prior to the
reset. The core always begins execution after reset from the base on the on-chip ROM. The
software in ROM will perform one of the several boot actions based on the value of Boot mode.
Note:
A COP reset via COP_RST does not alter these registers since a COP reset by
definition occurs unexpectedly during system operation, therefore possibly no longer
providing the required MODE inputs.
Note:
A software reset via RST_SW does not alter these registers, thereby allowing users to
reboot in a different mode without altering the hardware.
The 56800E core begins execution from the base of the on-chip ROM. The software in ROM will
perform one of several boot actions based on the value of BOOT MODE.
Some Boot modes, specifically those transferring code to internal PRAM for execution, require
header data to synchronize the peripheral, define the transfer start address in PRAM, and define
the number of words to load. The following four points describe the required format for boot
mode:
1. The four byte ASCII sequence BOOT (mode 1 only)
2. Two words (4 bytes) defining the number of program words to be loaded (modes 0, 1, 4, 5,
and 6 only)
Base + $0
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
Read
0
BOOT MODE
CHIP REV
0
EOnCE
EBL
CLKOUT
DBL
PRAM
DBL
DRAM
DBL
SW
RST
STOP
DBL
WAIT
DBL
Write
Reset
0
0
0
0
0
0
0
1
0
0
0
0
0
0
0
0