Rainbow Electronics T89C51AC2 - Manual (Page 4)

4
T89C51AC2
Rev. B – 19-Dec-01
Table 1. Pin Description
Pin Name Type Description
VSS GND Circuit ground.
VCC Supply Voltage.
VAREF Reference Voltage for ADC
VAGND Reference Ground for ADC
P0.0:7 I/O
Port 0:
Is an 8-bit open drain bi-directional I/O port. Port 0 pins that have 1’s written to them float, and in this state can be used
as high-impedance inputs. Port 0 is also the multiplexed low-order address and data bus during accesses to external
Program and Data Memory. In this application it uses strong internal pull-ups when emitting 1’s.
Port 0 also outputs the code bytes during program validation. External pull-ups are required during program
verification.
P1.0:7 I/O
Port 1:
Is an 8-bit bi-directional I/O port with internal pull-ups. Port 1 pins can be used for digital input/output or as analog
inputs for the Analog Digital Converter (ADC). Port 1 pins that have 1’s written to them are pulled high by the internal
pull-up transistors and can be used as inputs in this state. As inputs, Port 1 pins that are being pulled low externally will
be the source of current (I
IL
, see section "Electrical Characteristic") because of the internal pull-ups. Port 1 pins are
assigned to be used as analog inputs via the ADCCF register (in this case the internal pull-ups are disconnected).
As a secondary digital function, port 1 contains the Timer 2 external trigger and clock input; the PCA external clock
input and the PCA module I/O.
P1.0 / AN0 / T2
Analog input channel 0,
External clock input for Timer/counter2.
P1.1 / AN1 / T2EX
Analog input channel 1,
Trigger input for Timer/counter2.
P1.2 / AN2 / ECI
Analog input channel 2,
PCA external clock input.
P1.3 / AN3 / CEX0
Analog input channel 3,
PCA module 0 Entry of input/PWM output.
P1.4 / AN4 / CEX1
Analog input channel 4,
PCA module 1 Entry of input/PWM output.
P1.5 / AN5 / CEX2
Analog input channel 5,
PCA module 2 Entry of input/PWM output.
P1.6 / AN6 / CEX3
Analog input channel 6,
PCA module 3 Entry of input/PWM output.
P1.7 / AN7 / CEX4
Analog input channel 7,
PCA module 4 Entry ot input/PWM output.
Port 1 receives the low-order address byte during EPROM programming and program verification.
It can drive CMOS inputs without external pull-ups.