PD17012_15 Datasheet, PDF (245/320 Pages) Renesas Technology Corp – 4-BIT SINGLE-CHIP MICROCONTROLLERS WITH DIGITAL TUNING SYSTEM HARDWARE

µPD17012, 17P012
(1) Notes on using NPN transistor switch
When an NPN transistor switch is used, the low level may not be accurately read as illustrated in the figure
below.
VDD
High
RA
KS
Low
K
Internal resistor
RB
If KS is low and a high level is input to the base of the transistor
in the figure on the left, voltage VK input to K is as follows.
RB
VK =
× (VDD – VBE)
RA + RB
A low level must be input to K at this time because KS is low.
However, the voltage input to K changes depending on RA and
RB, as indicated by the above expression.
Therefore, a low level may not be input depending on the values
of RA and RB.
(2) Notes when diode A is not used
An example of a circuit where diode A is missing is shown below.
Suppose switches SW1 and SW2 are on, KS15 outputs a high level, and KS14 outputs a low level, as shown
below.
If diode A is missing, currents I1 and I2 indicated by the dotted lines flow.
Consequently, the high level of KS15 and low level of KS14 are not output correctly because of I2, and the key
input data of K3 cannot be accurately read.
If KS15 and KS14 are used to output LCD segment signals, the LCD cannot be turned on/off correctly.
SW1
SW2
LCD
I1
K2
K3
I2
Low
KS14
High
LCD
KS15
Data Sheet U10101EJ4V0DS
243