SAB80C517-M16 SIEMENS [Siemens Semiconductor Group], SAB80C517-M16 Datasheet - Page 90

• Manufacturer Part Number: SAB80C517-M16
• Description: 8-Bit CMOS Single-Chip Microcontroller
• Manufacturer: SIEMENS [Siemens Semiconductor Group]

The external reference voltage supply need only be applied when the A/D converter is used,
otherwise the pins
meet some requirements concerning the level of
supply voltage (see also "A/D Converter Characteristics" in the data sheet).
lf the above mentioned operating conditions are not met the accuracy of the converter may be
decreased.
Furthermore, the analog input voltage
(
which will also affect the accuracy of the other input channels.
7.4.3
A conversion is internally started by writing into special function register DAPR (ADEX = 0). A write-
to-DAPR will start a new conversion even if a conversion is currently in progress. The conversion
begins with the next machine cycle and the busy flag BSY will be set. When external start is
selected (ADEX = 1) the conversion starts in the machine cycle following the one where the low
level was detected at P6.0/ADST.
The conversion procedure is divided into three parts:
Load time (
During this time the analog input capacitance
voltage level. The external analog source needs to be strong enough to source the current to load
the analog input capacitance during the load time. This causes some restrictions for the impedance
of the analog source.
Sample time (
During this time the internal capacitor array is connected to the selected analog input channel. The
sample time includes the load time which is described above. After the load time has passed the
selected analog input must be held constant for the rest of the sample time. Otherwise the internal
calibration of the comparator circuitry could be affected which might result in a reduced accuracy of
the converter. However, in typical applications a voltage change of approx. 200 - 300 mV at the
inputs during this time has no effect.
Semiconductor Group
V
AREF
– The voltage
– The voltage
– The differential output impedance of the analog reference supply voltage should be less than
V
V
1 k .
+ 0.2 V). Otherwise, a static input current might result at the corresponding analog input
AREF
AGND
A/D Converter Timing
t
=
=
L
):
V
V
t
S
CC
SS
):
+/– 5 %
+ /– 0.2 V
V
V
V
AREF
AGND
AREF
must meet the following specification:
must meet a similar specification:
and
V
AGND
may be left unconnected. The reference voltage supply has to
V
AINPUT
C
must not exceed the range from (
I
(see data sheet) must be loaded to the analog input
91
V
AGND
On-Chip Peripheral Components
and
V
AREF
and the output impedance of the
V
AGND
– 0.2 V) to