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Section 8 I/O Ports
(HD404394 Series)
8.1
Overview
8.1.1
Features
The HD404394 Series I/O ports have the following features.
The HD404394 Series microcomputers have a total of 21 I/O pins, of which the three pins R1
0
to R1
2 are medium voltage NMOS open drain I/O pins. The five pins R13 and R20 to R23 are
standard voltage NMOS open drain I/O pins. The remaining 13 pins, D
0 to D5, R00 to R03, and
R3
1 to R33, are three state CMOS I/O pins. Of these pins, the pins D1, D2, and the R1 and R2
port pins are high current I/O pins that can each accept a current influx of up to 15 mA.
Certain I/O pins (D
0, D4, and the pins in the ports R0 and R3) are shared with the built-in
peripheral modules, such as timers and the serial interface. Setting these pins for use with the
built-in peripheral modules takes priority over their setting for use as D or R port pins.
Register settings are used to select input or output for I/O pins and to select the I/O port or
peripheral module usage for shared function pins.
All peripheral module output pins are CMOS outputs. However, the R0
2/SO pin can be
selected to be an NMOS open drain output by setting a register.
Since the system is reset in stop mode, the built-in peripheral module selections are cleared and
the I/O pins go to the high impedance state.
The CMOS output pins have built-in programmable pull-up MOS transistors. The on/off state
of these transistors can be controlled by register settings on an individual basis. Note that the
pull-up MOS transistor on/off settings are independent of the pin settings for use as built-in
peripheral module pins.
Table 8-1 provides an overview of the HD404394 Series port functions.