Precautions On Handling The Device - Fujitsu MB91319 Series Hardware Manual

CHAPTER 2 HANDLING THE DEVICE
2.1

Precautions on Handling the Device

This section contains information on preventing a latch up and on the handling of pins.
■ Preventing a Latch Up
A latch up can occur if, on a CMOS IC, a voltage higher than VCC or a voltage lower than VSS is
applied to an input or output pin or a voltage higher than the rating is applied between VCC and
VSS. A latch up, if it occurs, significantly increases the power supply current and may cause
thermal destruction of an element. When you use a CMOS IC, be very careful not to exceed the
maximum rating.
■ Unused Input Pins
Do not leave an unused input pin open, since it may cause a malfunction. Handle by, for
example, using a pull-up or pull-down resistor.
■ Power Supply Pins
If more than one VCC or VSS pin exists, those that must be kept at the same potential are
designed to be connected to one other inside the device to prevent malfunctions such as latch up.
Be sure to connect the pins to a power supply and ground external to the device to minimize
undesired electromagnetic radiation, prevent strobe signal malfunctions due to an increase in
ground level, and conform to the total output current rating. Given consideration to connecting the
current supply source to VCC and VSS of the device at the lowest impedance possible.
It is also recommended that a ceramic capacitor of around 0.1 µF be connected between VCC
and VSS at circuit points close to the device as a bypass capacitor.
■ Quartz Oscillation Circuit
Noise near the X0 or X1 pin may cause the device to malfunction. Design printed circuit boards
so that X0, X1, the quartz oscillator (or ceramic oscillator), and the bypass capacitor to ground
are located as near to one another as possible.
It is strongly recommended that printed circuit board artwork that surrounds the X0 and X1 pins
with ground be used to increase the expectation of stable operation.
Please ask the crystal maker to evaluate the oscillation characteristics of the crystal and this
device.
■ Mode Pins (MD0 to MD3)
These pins must be directly connected to VCC or VSS when they are used. Keep the pattern
length between a mode pin on a printed circuit board and VCC or VSS as short as possible so
that they can be connected at a low impedance.
■ Tool Reset Pins (TRST)
Be sure to input the same signal as the INIT, when this pin is not used for the tool. The same
processing is executed for the product.
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