M054LAN Datasheet, PDF (33/64 Pages) Nuvotem Talema – ARM Cortex™-M0 32-BIT MICROCONTROLLER

64M052/M054 Data Sheet
Port Latch
N
Data
Port Pin
Input Data
Figure 6–11 Open-Drain Output
6.4.1.4 Quasi-bidirectional Mode Explanation
Set Px_PMD(PMDn[1:0]) to 2’b11 the Px[n] pin is in Quasi-bidirectional mode and the I/O pin
supports digital output and input function at the same time but the source current is only up to
hundreds uA. Before the digital 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 drive a “low”
output on 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 takes. If pin state is low, then pin will drive strong high
with 2 clock cycles on the pin and then disable the strong output drive and then the pin status is
control by internal pull-up resistor. Note that the source current capability in quasi-bidirectional
mode is only about 200uA to 30uA for VDD is form 5.0V to 2.5V
VDD
Port Latch
Data
2 CPU
Clock Delay
P _Strong P
Very
Weak
P _Weak
N
Port Pin
Input Data
Figure 6–12 Quasi-bidirectional I/O Mode
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Publication Release Date: Mar 15, 2011
Revision V1.0