Ac Electrical Specifications Definitions - Motorola M68000 User Manual

is lost through the active P-channel transistor. Also, since only one transistor is turned on
during the steady state, power consumption is determined by leakage currents.
Because the basic CMOS cell is composed of two complementary transistors, a virtual
semiconductor controlled rectifier (SCR) may be formed when an input exceeds the
supply voltage. The SCR that is formed by this high input causes the device to become
latched in a mode that may result in excessive current drain and eventual destruction of
the device. Although the MC68HC000 and MC68EC000 is implemented with input
protection diodes, care should be exercised to ensure that the maximum input voltage
specification is not exceeded. Some systems may require that the CMOS circuitry be
isolated from voltage transients; other may require additional circuitry.
The MC68HC000 and MC68EC000, implemented in CMOS, is applicable to designs to
which the following considerations are relevant:
1. The MC68HC000 and MC68EC000 completely satisfies the input/output drive
requirements of CMOS logic devices.
2. The HCMOS MC68HC000 and MC68EC000 provides an order of magnitude
reduction in power dissipation when compared to the HMOS MC68000. However,
the MC68HC000 does not offer a "power-down" mode.
10.5 AC ELECTRICAL SPECIFICATION DEFINITIONS
The AC specifications presented consist of output delays, input setup and hold times, and
signal skew times. All signals are specified relative to an appropriate edge of the clock and
possibly to one or more other signals.
The measurement of the AC specifications is defined by the waveforms shown in Figure
10-2. To test the parameters guaranteed by Motorola, inputs must be driven to the voltage
levels specified in the figure. Outputs are specified with minimum and/or maximum limits,
as appropriate, and are measured as shown. Inputs are specified with minimum setup and
hold times, and are measured as shown. Finally, the measurement for signal-to-signal
specifications are shown.
The testing levels used to verify conformance to the AC
specifications does not affect the guaranteed DC operation of
the device as specified in the DC electrical characteristics.
MOTOROLA M68000 8-/16-/32-BIT MICROPROCESSORS USER'S MANUAL
Freescale Semiconductor, Inc.
NOTE
For More Information On This Product,
Go to: www.freescale.com
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