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MC68F375
SINGLE-CHIP INTEGRATION MODULE 2 (SCIM2E)
MOTOROLA
REFERENCE MANUAL
Rev. 25 June 03
4-58
cycles take. Worst case occurs in slow reference mode and is approximately 15 milli-
seconds. During this period, MCU pins may be in an indeterminate state. While pull-
up resistors may be used on input only pins, active logic will be required to condition
input/output or output only pins.
Figure 4-18 depicts the timing of the power-on reset sequence.
Figure 4-18 Power-On Reset
4.7.7 Pin State During Reset
It is important to keep the distinction between pin function and pin electrical state clear.
Although control register values and mode select inputs determine pin function, a pin
driver can be active, inactive, or in a high impedance state when reset occurs. During
power-on reset, pin state is subject to the constraints discussed in 4.7.6 Power-On NOTE
Pins that are not used should either be configured as outputs (if pos-
sible) or as inputs and be pulled to an appropriate inactive state. This
decreases unnecessary current consumption caused by digital
inputs floating near mid-supply level.
4.7.7.1 Reset States of SCIM2E Pins
Generally, while RESET is asserted, SCIM2E pins either go into a high-impedance
state or are driven to their inactive states. Operating mode selection occurs when
SCIM2E POR TIM
CLKOUT
VCO
LOCK
BUS
CYCLES
RESET
VDD
NOTES:
5. INTERNAL START-UP TIME.
6. FIRST INSTRUCTION FETCHED.
ADDRESS AND
CONTROL SIGNALS
THREE-STATED
BUS STATE
UNKNOWN
4
1
3
2
5
6
1. TWO CLOCK CYCLE DELAY REQUIRED BY RESET CONTROL LOGIC TO SWITCH RESET PIN FROM INPUT TO OUTPUT.
2. RESET CONTROL LOGIC DRIVES THE RESET PIN LOW FOR 512 CLOCK CYCLES TO GUARANTEE THIS LENGTH OF RESET TO THE ENTIRE SYSTEM.
3. TEN CLOCK CYCLE DELAY DURING WHICH THE RESET PIN IS NO LONGER DRIVEN AND IS ALLOWED TO RISE TO A LOGIC ONE. OPERATING
LATCHED FROM DATA[15:0] AND BERR WHEN THIS DELAY BEGINS.
4. ADDITIONAL 180 CLOCK DELAY PROVIDED BY RESET CONTROL LOGIC TO ALLOW THE RESET PIN TO RISE TO A LOGIC ONE IF IT DID NOT DO SO DURING
THE PRIOR 10 CLOCK CYCLES.
CONFIGURATION IS
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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