MC9S12KG128_10 Datasheet, PDF (456/606 Pages) Freescale Semiconductor, Inc – HCS12 Microcontrollers

Chapter 15 Background Debug Module (BDMV4) Block Description
Table 15-2. BDMSTS Field Descriptions (continued)
Field
2
CLKSW
1
UNSEC
Description
Clock Switch — The CLKSW bit controls which clock the BDM operates with. It is only writable from a hardware
BDM command. A 150 cycle delay at the clock speed that is active during the data portion of the command will
occur before the new clock source is guaranteed to be active. The start of the next BDM command uses the new
clock for timing subsequent BDM communications.
Table 15-3 shows the resulting BDM clock source based on the CLKSW and the PLLSEL (Pll select from the
clock and reset generator) bits.
Note: The BDM alternate clock source can only be selected when CLKSW = 0 and PLLSEL = 1. The BDM serial
interface is now fully synchronized to the alternate clock source, when enabled. This eliminates frequency
restriction on the alternate clock which was required on previous versions. Refer to the device overview
section to determine which clock connects to the alternate clock source input.
Note: If the acknowledge function is turned on, changing the CLKSW bit will cause the ACK to be at the new rate
for the write command which changes it.
Unsecure — This bit is only writable in special single-chip mode from the BDM secure firmware and always gets
reset to zero. It is in a zero state as secure mode is entered so that the secure BDM firmware lookup table is
enabled and put into the memory map along with the standard BDM firmware lookup table.
The secure BDM firmware lookup table verifies that the on-chip EEPROM and FLASH EEPROM are erased. This
being the case, the UNSEC bit is set and the BDM program jumps to the start of the standard BDM firmware
lookup table and the secure BDM firmware lookup table is turned off. If the erase test fails, the UNSEC bit will
not be asserted.
0 System is in a secured mode
1 System is in a unsecured mode
Note: When UNSEC is set, security is off and the user can change the state of the secure bits in the on-chip
FLASH EEPROM. Note that if the user does not change the state of the bits to “unsecured” mode, the
system will be secured again when it is next taken out of reset.
PLLSEL
0
0
1
1
CLKSW
0
1
0
1
Table 15-3. BDM Clock Sources
BDMCLK
Bus clock
Bus clock
Alternate clock (refer to the device overview chapter to determine the alternate clock
source)
Bus clock dependent on the PLL
MC9S12KG128 Data Sheet, Rev. 1.16
456
Freescale Semiconductor