Rainbow Electronics AT83C21GC - Manual (Page 5)

5
4247CS–SCR–11/05
AT83C21GC
P3.6 CCLK1 DV
CC
O
LED function
These pins can be directly connected to the cathode of the standard LED without
external current limiting resistors. The typical current of each output can be
programmed by software to 2, 4 or 10 mA (LEDCON register).
P3.7 CRST1 DV
CC
I/O
Input/Output Function
P3.7 is a bi-directional I/O port with internal pull-ups.
RST V
CC
I/O Reset Input
Holding this pin low for 64 oscillator periods while the oscillatoris running resets the
device. The Port pins are driven to their reset conditions when a voltage lower than V
IL
is applied, whether or not the oscillator is running. This pin has an internal pull-up
resistor which allows the device to be reset by connecting a capacitor between this pin
and VSS. Asserting RST when the chip is in Idle mode or Power-down mode returns
the chip to normal operation. The output is active for at least 12 oscillator periods when
an internal reset occurs.
XTAL1 V
CC
I Input to the on-chip Inverting Oscillator Amplifier
To use the internal oscillator, a crystal/resonator circuit is connected
to this pin. If an external oscillator is used, its output is connected to this pin.
XTAL2 V
CC
O Output of the on-chip Inverting Oscillator Amplifier
To use the internal oscillator, a crystal/resonator circuit is connected
to this pin. If an external oscillator is used, XTAL2 may be left unconnected.
V
CC
PWR Supply Voltage
V
CC
is used to power the internal voltage regulators and internal I/O’s.
LI PWR DC/DC Input
LI must be tied to V
CC
through an external coil (typically 4, 7 μH) and provide the
current for the pump charge of the DC/DC converter.
CV
CC
PWR Card Supply Voltage
CV
CC
is the programmable voltage output for the Card interface. It must be connected
to an external decoupling capacitor.
DV
CC
PWR Digital Supply Voltage
DV
CC
is used to supply the digital core and internal I/Os. It is internally connected to the
output of a 3V regulator and must be connected to an external decoupling capacitor.
EV
CC
V
CC
PWR Extra Supply Voltage
EV
CC
is used to supply the level shifters of UART interface I/O pins. It must be
connected to an external decoupling capacitor. This reference voltage is generated
internally (automatically or not), or it can be connected to an external voltage
reference.
CVSS GND DC/DC Ground
CVSS is used to sink high shunt currents from the external coil.
VSS GND Ground
Table 1. Port Signal Description (Continued)
Port
Signal
Name
Internal
Power
Supply ESD Type Description