ISD91200 Series Technical Reference Manual
Release Date: Sep 16, 2019
- 134 -
Revision 2.4
5.4.2.3
Open-Drain Mode
For Px_MODE
n =
10b the GPIO
x
port [
n
] pin is in Open-Drain mode. The GPIO pin supports a digital
output function but only with sink current capability, an additional pull-up resister is needed for defining
a high state. If the bit value in the corresponding bit [n] of Px_DOUT is “0”, pin is driven low. If the bit
value in the corresponding bit [n] of Px_DOUT is “1”, the pin state is defined by the external load on the
pin.
P ort P in
P ort La tch
Da ta
N
Input Da ta
Figure 5-7 Open-Drain Output
5.4.2.4
Quasi-bidirectional Mode Explanation
For Px_MODE
n =
11b the GPIO
x
port [
n
] pin is in Quasi-bidirectional mode and the I/O pin supports
digital output and input function where the source current is only between 30-200uA.Before input
function is performed the corresponding bit in Px_DOUT must be set to 1. The quasi-bidirectional
output is common on the 80C51 and most of its derivatives. If the bit value in the corresponding bit [n]
of Px_DOUT is “0”, the pin will drive a “low” output to the pin. If the bit value in the corresponding bit [n]
of Px_DOUT is “1”, the pin will check the pin value. If pin value is high, no action is taken. If pin state is
low, then pin will drive a strong high for2 clock cycles. After this the pin has an internal pull-up resistor
connected. Note that the source current capability in quasi-bidirectional mode is approximately200uA to
30uA for VDD form 5.0V to 2.4V.
P ort P in
2 CP U
Clock De la y
Input Da ta
P ort La tch
Da ta
P
P
P
N
VDD
S trong
Ve ry
We a k
We a k
Figure 5-8 Quasi-bidirectional GPIO Mode
