38K0 Datasheet, PDF (109/133 Pages) Mitsubishi Electric Semiconductor – SINGLE-CHIP 8-BIT CMOS MICROCOMPUTER

38K0 Group
NOTES ON USAGE
Power Source Voltage
When the power source voltage value of a microcomputer is less
than the value which is indicated as the recommended operating
conditions, the microcomputer does not operate normally and may
perform unstable operation.
In a system where the power source voltage drops slowly when
the power source voltage drops or the power supply is turned off,
reset a microcomputer when the power source voltage is less than
the recommended operating conditions and design a system not
to cause errors to the system by this unstable operation.
Handling of Power Source Pin
In order to avoid a latch-up occurrence, connect a capacitor suit-
able for high frequencies as bypass capacitor between power
source pin (Vcc pin) and GND pin (Vss pin). Besides, connect the
capacitor to as close as possible. For bypass capacitor which
should not be located too far from the pins to be connected, a ce-
ramic or electrolytic capacitor of 1.0 µF is recommended.
USB Port Pins (D0+, D0-) Treatment
•The USB specification requires a driver-impedance 28 to 44 Ω. In
order to meet the USB specification impedance requirements,
connect a resistor (27 Ω recommended) in series to the USB port
pins.
In addition, in order to reduce the ringing and control the falling/
rising timing and a crossover point, connect a capacitor between
the USB port pins and the Vss pin if necessary.
The values and structure of those peripheral elements depend on
the impedance characteristics and the layout of the printed circuit
board. Accordingly, evaluate your system and observe waveforms
before actual use and decide use of elements and the values of
resistors and capacitors.
•Make sure the USB D+/D- lines do not cross any other wires.
Keep a large GND area to protect the USB lines. Also, make sure
you use a USB specification compliant connecter for the connec-
tion.
USBVREF pin Treatment (Noise Elimination)
•Connect a capacitor between the USBVREF pin and the Vss pin.
The capacitor should have a 2.2 µF capacitor (electrolytic capaci-
tor) and a 0.1 µF capacitor (ceramic type capacitor) connected in
parallel.
•In Vcc = 3.0 to 3.6 V operation, connect the USBVREF pin directly
to the Vcc pin in order to supply power to the USB port circuit. In
addition, you will need to disable the built-in USB reference volt-
age circuit in this operation (set bit 4 of the USB control register
to “0”.) If you are using the bus powered supply in this condition,
the DC-DC converter must be placed outside the MCU.
•In Vcc = 4.00 to 5.25 V operation, do not connect the external
DC-DC converter to the USBVREF pin. Use the built-in USB refer-
ence voltage circuit.
USB Communication
In applications requiring high-reliability, we recommend providing
the system with protective measures such as USB function initial-
ization by software or USB reset by the host to prevent USB
communication from being terminated unexpectedly, for example
due to external causes such as noise.
Flash Memory Version
The CNVss pin is connected to the internal memory circuit block
by a low-ohmic resistance, since it has the multiplexed function to
be a programmable power source pin (VPP pin) as well.
To improve the noise reduction, connect a track between CNVss
pin and Vss pin or Vcc pin with 1 to 10 kΩ resistance.
The mask ROM version track of CNVss pin has no operational in-
terference even if it is connected to Vss pin or Vcc pin via a
resistor.
Electric Characteristic Differences Between
Mask ROM and Flash Memory Version MCUs
There are differences in electric characteristics, operation margin,
noise immunity, and noise radiation between Mask ROM and
Flash Memory version MCUs due to the difference in the manufac-
turing processes.
When manufacturing an application system with the Flash
Memory version and then switching to use of the Mask ROM ver-
sion, please perform sufficient evaluations for the commercial
samples of the Mask ROM version.
DATA REQUIRED FOR MASK ORDERS
The following are necessary when ordering a mask ROM produc-
tion:
1. Mask ROM Order Confirmation Form^✽
2. Mark Specification Form^✽
3. Data to be written to ROM, in EPROM form (three identical cop-
ies) or one floppy disk.
✽ For the mask ROM confirmation and the mark specifications, re-
fer to the “Renesas Technology Corp.” Homepage
(http://www.renesas.com).
Rev.3.00 Oct 05, 2006 page 109 of 129
REJ03B0192-0300