Fujitsu F2MC-16LX Hardware Manual page 38

CHAPTER 1 OVERVIEW
❍ Cautions on using an external clock
When using an external clock, use only the X0 pin and leave the X1 pin open.
❍ Handling power supply pins (Vcc/Vss)
If there are multiple power supply pins (Vcc/Vss), pins to which the same voltage is applied are
designed to be connected to each other in order to prevent malfunctions such as latchup.
Confirm that all of these pins are externally connected to the power supply or ground to reduce
undesired radiation, prevent malfunction of the strobe signal because of ground level increase,
and maintain the total output current standard.
Also, connect the Vcc and Vss pins of this device to a current supply with the lowest possible
impedance.
In addition, it is recommended to connect a condenser of about 0.1
by-pass condenser for this device.
❍ Crystal oscillator circuit
Noise around the X0 or X1 pins may cause device malfunction. When designing a printed-
circuit board, confirm that the X0 and X1 pins, a crystal oscillator (ceramic oscillator), and by-
pass condenser to the ground are located as close to the device as possible, and that the
number of cables crossing other cables is as low as possible.
Also, it is highly recommended to use a printed-circuit board artwork surrounding the X0 and X1
pins to stabilize the operation of the device.
❍ Procedure for turning on the A/D converter power supply and the analog input
Confirm that the digital power supply (Vcc) is turned on before turning the power supplies of the
A/D converter (AVcc, AVRH, AVRL) and applying analog input (AN0 to AN7).
Moreover, when shutting down power supplies, turn off the digital power supply only after
turning off the power supplies of the A/D converter and the analog input. Confirm that AV
does not exceed AVcc when turning the power supplies on or off (The analog power supply and
the digital power supply can be turned on or off at the same time).
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Figure 1.8-1 Method of Using an External Clock
OPEN
Figure 1.8-2 Handling Power Supply Pins (Vcc/Vss)
Vcc
Vss
MB90550A/B
Vcc
Series
Vss
MB90550A/B Series
X0
X1
Vss
Vcc
Vss
Vcc
Vcc
Vss
µ
F between Vcc and Vss as
RH