MC68CK331CAG16 Datasheet, PDF (38/84 Pages) Freescale Semiconductor, Inc – 32-Bit Modular Microcontroller

Freescale Semiconductor, Inc.
Module
CPU32
GPT
QSM
Table 19 Module Pin Functions
Pin Mnemonic
DSI/IFETCH
DSO/IPIPE
BKPT/DSCLK
PGP7/IC4/OC5
PGP[6:3]/OC[4:1]
PGP[2:0]/IC[3:1]
PAI
PCLK
PWMA, PWMB
PQS7/TXD
PQS[6:4]/PCS[3:1]
PQS3/PCS0/SS
PQS2/SCK
PQS1/MOSI
PQS0/MISO
RXD
Function
DSI/IFETCH
DSO/IPIPE
BKPT/DSCLK
Discrete Input
Discrete Input
Discrete Input
Discrete Input
Discrete Input
Discrete Output
Discrete Input
Discrete Input
Discrete Input
Discrete Input
Discrete Input
Discrete Input
RXD
3.7.3 Reset Timing
The RESET input must be asserted for a specified minimum period in order for reset to occur. External
RESET assertion can be delayed internally for a period equal to the longest bus cycle time (or the bus
monitor time-out period) in order to protect write cycles from being aborted by reset. While RESET is
asserted, SIM pins are either in a disabled high-impedance state or are driven to their inactive states.
When an external device asserts RESET for the proper period, reset control logic clocks the signal into
an internal latch. The control logic drives the RESET pin low for an additional 512 CLKOUT cycles after
it detects that the RESET signal is no longer being externally driven, to guarantee this length of reset
to the entire system.
If an internal source asserts a reset signal, the reset control logic asserts RESET for a minimum of 512
cycles. If the reset signal is still asserted at the end of 512 cycles, the control logic continues to assert
RESET until the internal reset signal is negated.
After 512 cycles have elapsed, the reset input pin goes to an inactive, high-impedance state for 10 cy-
cles. At the end of this 10-cycle period, the reset input is tested. When the input is at logic level one,
reset exception processing begins. If, however, the reset input is at logic level zero, the reset control
logic drives the pin low for another 512 cycles. At the end of this period, the pin again goes to high-
impedance state for 10 cycles, then it is tested again. The process repeats until RESET is released.
3.7.4 Power-On Reset
When the SIM clock synthesizer is used to generate the system clock, power-on reset involves special
circumstances related to application of system and clock synthesizer power. Regardless of clock
source, voltage must be applied to clock synthesizer power input pin V_DDSYN in order for the MCU to
operate. The following discussion assumes that V_DDSYN is applied before and during reset. This mini-
mizes crystal start-up time. When V_DDSYN is applied at power-on, start-up time is affected by specific
crystal parameters and by oscillator circuit design. V_DD ramp-up time also affects pin state during reset.
During power-on reset, an internal circuit in the SIM drives the internal (IMB) and external reset lines.
The circuit releases the internal reset line as V_DD ramps up to the minimum specified value, and SIM
pins are initialized. When V_DD reaches the specified minimum value, the clock synthesizer VCO begins
operation. Clock frequency ramps up to the specified limp mode frequency. The external RESET line
remains asserted until the clock synthesizer PLL locks and 512 CLKOUT cycles elapse.
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