HD404459 Datasheet, PDF (57/122 Pages) Renesas Technology Corp – 4-bit HMCS400-series microcomputers

HD404459 Series
Pull-Up MOS Transistor Control: A program-controlled pull-up MOS transistor is provided for each
input/output pin other than input-only pins D₁₀, D₁₁, R9₃, and RA₀–RA₃. The on/off status of all these
transistors is controlled by bit 3 (MIS3) of the miscellaneous register (MIS: $00C), and the on/off status of
an individual transistor can also be controlled by the port data register (PDR) of the corresponding pin—
enabling on/off control of that pin alone (table 23 and figure 39).
The on/off status of each transistor and the peripheral function mode of each pin can be set independently.
Miscellaneous register (MIS: $00C)
Bit
3
2
1
Initial value
0
0
0
Read/Write
W
W
W
Bit name
MIS3 MIS2 MIS1
0
0
W
MIS0
MIS3
0
1
Pull-up MOS
on/off selection
Off
On
MIS2
0
1
CMOS buffer
on/off selection
for pin R4₃/SO
On
Off
MIS1
MIS0
t_RC selection.
Refer to figure 18 in the
operation modes section.
Figure 39 Miscellaneous Register (MIS)
How to Deal with Unused I/O Pins: I/O pins that are not needed by the user system (those that remain
floating) must be connected to V_CC to prevent LSI malfunctions due to noise. These pins must either be
pulled up to V_CC by their pull-up MOS transistors or by resistors of about 100 kΩ.
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