Maxim Integrated MAXQ622 - Manual (Page 27)

MAXQ612/MAXQ622 User’s Guide
Maxim Integrated 2-23
2.6.8 Disabling MAXQ612/MAXQ622-Specific Memory Access Features
The MAXQ612/MAXQ622 memory-protection features are specific to the MAXQ612/MAXQ622 family of parts and can
cause some confusion in the way that they impact debugging and bootloader commands when compared to MAXQ
parts . To enable users to develop initial firmware as quickly as possible, the following code can be added to your
application code to disable the memory protection features and allow code loading and debugging in the same man-
ner as previous parts:
ORG 0
Jump Start
ORG 000eh
Debug_Lockout:
DW 0ffffh ; disable debug lockout
ORG 000fh
ULDR_PageNumber:
DW 0ffffh ; do not define a user loader page
ORG 0010h
System_PassworD:
DW offffh,offffh, offffh,offffh, offffh,offffh, offffh,offffh
DW offffh,offffh, offffh,offffh, offffh,offffh, offffh,offffh
ORG 0020h
; interrupt vectors go here
ORG 0100h
Start:
; Your application code here
;…
END
Once the memory-protection features are fully understood, this code can be removed from the user’s application code
to enable memory access control .
2.7 Clock Generation
All functional modules in the MAXQ612/MAXQ622 are synchronized to a single system clock with the exception of the
wake-up timer . The internal clock circuitry generates the system clock from one of two possible sources:
• Internal oscillator, using an external crystal or resonator
• External clock signal
The external clock and crystal are mutually exclusive since they are input through the same clock pin . Each time code
execution must start or restart (as can be the case when exiting stop mode) using the external clock source, the fol-
lowing sequence occurs:
• Reset the crystal warmup counter.
• Allow the required warmup delay: 8192 external clock cycles if exiting from stop mode.
• Code execution starts after the crystal warmup sequence.
2.7.1 External Clock (Crystal/Resonator)
An external quartz crystal or a ceramic resonator can be connected from HFXIN to HFXOUT determining the frequency,
as illustrated in Figure 2-10 . The fundamental mode of the crystal operates as inductive reactance in parallel resonance
with external capacitance to the crystal .