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MC68341 USER’S MANUAL
MOTOROLA
4.5 MC68340 INITIALIZATION SEQUENCE
The following paragraphs discuss a suggested method for initializing the MC68341 after
power-up.
4.5.1 Startup
RESET is asserted by the MC68341 during the time in which VCC is ramping up, the VCO
is locking onto the frequency, and the MC68341 is going through the reset operation. After
RESET is negated, four bus cycles are run, with global CS0 being asserted to fetch the
32-bit supervisor stack pointer (SSP) and the 32-bit program counter (PC) from the boot
ROM. Until programmed, CS0 is a global, 16-bit port, six-wait-state chip select. CS0 can
be programmed to continue decode for a range of addresses after the V-bit is set,
provided the desired address range is first loaded into the CS0 base address register.
After the V-bit is set for CS0 , global chip select can only be restarted with a system reset.
After the SSP and the PC are fetched, the module base address register (MBAR) should
be initialized, and the MBAR V-bit should be set (CPU space address $0003FF00) with
the desired base address for the internal modules.
4.5.2 SIM41 Module Configuration
The order of the following SIM41 register initializations is not important; however, time can
be saved by initializing the SYNCR first to quickly increase to the desired processor
operating frequency. The module base address register must be initialized prior to any of
following steps.
Clock Synthesizer Control Register (SYNCR):
Set frequency control bits (W, X, Y, Z) to specify frequency.
Select action taken during loss of crystal (RSTEN bit): activate a system reset or
operate in limp mode.
Select system clock and CLKOUT during LPSTOP (STSIM and STEXT bits).
Module Configuration Register (MCR)
If using the software watchdog, periodic interrupt timer, and/or the bus monitor, select
action taken when FREEZE is asserted (FRZx bits).
Select AVEC/CS0 configuration (AVEC bit).
Select the access privilege for the supervisor/user registers (SUPV bit).
Select the interrupt arbitration level for the SIM41 (IARBx bits).
Autovector Register (AVR)
Select the desired external interrupt levels for internal autovectoring.
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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