Signal Descriptions
MCF5272 ColdFire Integrated Microprocessor User’s Manual, Rev. 3
Freescale Semiconductor
19-23
19.6.12 SDRAM Bank Selects (SDBA[1:0])
These outputs are the SDRAM bank select signals.
19.6.13 SDRAM Row Address 10 (A10)/A10 Precharge (A10_PRECHG)
This output is the SDRAM row address 10 and the precharge strobe.
19.7
CPU Clock and Reset Signals
This section describes clock and reset signals in the CPU.
19.7.1
RSTI
RSTI is the primary reset input to the device. Asserting RSTI immediately resets the CPU and peripherals.
However, the reset of the SDRAM controller and hence SDRAM contents depend on DRESETEN.
Asserting RSTI also causes RSTO to be asserted for 32K CPU clock cycles.
19.7.2
DRESETEN
DRESETEN is asserted to indicate that the SDRAM controller is to be reset whenever RSTI asserts. If
DRESETEN is high, RSTI does not affect the SDRAM controller, which continues to refresh external
memory. This is useful for debug situations where a reset of the device is required without losing data
located in SDRAM. DRESETEN is normally tied high or low depending on system requirements. It should
never be tied to RSTI or RSTO.
19.7.3
CPU External Clock (CLKIN)
CLKIN should be connected to an external clock oscillator. The CLKIN input frequency can range from
DC to 66 MHz. The frequency input to this signal must be greater than twice the frequency applied at E_Tx
CLK. The clock frequency applied to CLKIN must exceed 24 MHz when the system uses a USB
peripheral.
19.7.4
Reset Output (RSTO)
Reset output (RSTO) is driven low for 128 CPU clocks when the soft reset bit of the system configuration
register (SCR[SOFTRST]) is set. It is driven low for 32K CPU clocks when the software watchdog timer
times out or when a low input level is applied to RSTI.
19.8
Interrupt Request Inputs (INT[6:1])
The six interrupt request inputs (INT[6:1]) can generate separate, maskable interrupts on negative edge
(high to low) or positive edge (low to high) transitions. In addition to the triggering edge being
programmable, the priority can also be programmed. Each interrupt input has a separate programmable
interrupt level.