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XC2200 Derivatives
System Units (Vol. 1 of 2)
Dedicated Pins
User’s Manual
8-2
V2.1, 2008-08
DediPins_X7, V2.0
The Oscillator Input XTAL1 and Output XTAL2
connect the internal
Main Oscillator
to the external crystal. The oscillator provides an inverter and a feedback element. The
standard external oscillator circuitry comprises the crystal, two low end capacitors and
series resistor to limit the current through the crystal. The main oscillator is intended for
the generation of a high-precision operating clock signal for the XC2200.
An external clock signal may be fed to the input XTAL1, leaving XTAL2 open. The current
logic state of input XTAL1 can be read via a status flag, so XTAL1 can be used as digital
input if neither the oscillator interface nor the clock input is required.
Note: Pin XTAL1 belongs to the core power domain DMP_M. All input signals, therefore,
must be within the core voltage range.
The Test Mode Input TESTM
puts the XC2200 into a test mode, which is used during
the production tests of the device. In test mode, the XC2200 behaves different from
normal operation. Therefore, pin TESTM must be held HIGH (connect to
V
DDPB
) for
normal operation in an application system.
The Test Reset Input TRST
puts the XC2200’s debug system into reset state. During
normal operation this input should be held low. For debugging purposes the on-chip
debugging system can be enabled by driving pin TRST high at the rising edge of PORST.
The Control Pin for Core Voltage Generation TRef
was used to control the generation
method for the core supply voltage
V
DDI
in step AA. For that step, pin TRef must be
connected to
V
DDPB
(use the on-chip EVRs).
This connection is no more required from step AB on. For the current step, pin TRef is
logically not connected.
Future derivatives will feature an additional general purpose IO pin at this position.
The Analog Reference Voltage Supply pins
V
AREFx
and
V
AGND
provide separate
reference voltage for the on-chip Analog/Digital-Converter(s). This reduces the noise
that is coupled to the analog input signals from the digital logic sections and so improves
the stability of the conversion results, when
V
AREF
and
V
AGND
are properly discoupled
from
V
DD
and
V
SS
. Also, because conversion results are generated in relation to the
reference voltages, ratiometric conversions are easily achieved.
Note: Channel 0 of each module can be used as an alternate reference voltage input.
The Core Supply pins
V
DDIM
/
V
DDI1
serve two purposes: While the on-chip EVVRs
provide the power for the core logic of the XC2200 these pins connect the EVVRs to their
external buffer capacitors. For external supply, the core voltage is applied to these pins.
The respective
V
DDI
/
V
SS
pairs should be decoupled as close to the pins as possible. Use
ceramic capacitors and observe their values recommended in the respective Data
Sheet.