MC68340 datasheet(133/441 Pages) FREESCALE

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MC68340 USER’S MANUAL

MOTOROLA

4.4 MC68340 INITIALIZATION SEQUENCE

The following paragraphs discuss a suggested method for initializing the MC68340 after

power-up.

4.4.1 Startup

RESET is asserted by the MC68340 during the time in which VCC is ramping up, the VCO

is locking onto the frequency, and the MC68340 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 differently,

CS0 is a global, 16-bit-wide, three-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

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.

4.4.2 SIM40 Module Configuration

The order of the following SIM40 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) 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 port B configuration (FIRQ bit). Note that this bit is used in combination with

the bits in the PPARB to program the function of the port B pins.

• Select the access privilege for the supervisor/user registers (SUPV bit).

• Select the interrupt arbitration level for the SIM40 (IARBx bits).

Autovector Register (AVR)

• Select the desired external interrupt levels for internal autovectoring.

Freescale Semiconductor, Inc.

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