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11. I/O Ports 
Port1 
Port 1 is an 8-bit bi-directional I/O port with internal pull-ups. Port 1 output buffers can sink/source four external TTL 
device inputs. When port 1 pins are written as 1’s, these pins are pulled high by the internal pull-ups and can be used as 
inputs. As inputs, Port 1 pins that are externally being pulled low will source current because of the internal pull-ups. 
Port 1 also serves the analog signal input of A/D converter, as listed below: 
P1.0 ADI0 (analog input signal channel 0) 
P1.1 ADI1 (analog input signal channel 1) 
P1.2 ADI2 (analog input signal channel 2) 
P1.3 ADI3 (analog input signal channel 3) 
P1.4 ADI4 (analog input signal channel 4) 
P1.5 ADI5 (analog input signal channel 5) 
P1.6 ADI6 (analog input signal channel 6) 
P1.7 ADI7 (analog input signal channel 7) 
Port2.0, 2.1, 2.3 
Port2.0, 2.1, 2.3 are a bi-directional I/O port with internal pull-ups. Port2.0, 2.1, 2.3 output buffers can sink/source four 
external TTL device inputs. When Port2.0, 2.1, 2.3 pins are written as 1’s, these pins are pulled high by the internal pull-ups 
and can be used as inputs. As inputs, Port2.0, 2.1, 2.3 pins that are externally being pulled low will source current because of 
the internal pull-ups.  
Port 2.0 also serves the output signal of PWM 2. 
Port 3 
Port 3 is an 8-bit bi-directional I/O port with internal pull-ups. Port 3 output buffers can sink/source four external TTL 
device inputs. When port 3 pins are written as 1’s, these pins are pulled high by the internal pull-ups and can be used as 
inputs. As inputs, Port 3 pins that are externally being pulled low will source current because of the internal pull-ups. 
Port 3 also serves the functions of various special features, as listed below: 
P3.0 RXD (serial input port) 
P3.1 TXD (serial output port) 
P3.2 INT0 (external interrupt 0) 
P3.3 INT1 (external interrupt 1) 
P3.4 T0 (timer 0 external input) 
P3.5 T1 (timer 1 external input) 
P3.6 PWM1 (PWM 1 signal output) 
P3.7 VREF (external reference voltage input for ADC) 
                 T81L0006A/B
TM Technology Inc. reserves the right 
P. 21               
Publication Date: AUG. 2005 
to change products or specifications without notice.                                 Revsion : B