
Semiconductor Group
76
On-Chip Peripheral Components
7.4.2
Reference Voltages
The SAB 80(C)515 has two pins to which a reference voltage range for the on-chip A/D converter
is applied (pin
V
AREF
for the upper voltage and pin
V
AGND
for the lower voltage). In contrast to
conventional A/D converters it is now possible to use not only these externally applied reference
voltages for the conversion but also internally generated reference voltages which are derived from
the externally applied ones. For this purpose a resistor ladder provides 16 equidistant voltage levels
between
V
AREF
and
V
AGND
. These steps can individually be assigned as upper and lower reference
voltage for the converter itself. These internally generated reference voltages are called
V
lntAREF
and
V
lntAGND
. The internal reference voltage programming can be thought of as a programmable "D/A
converter" which provides the voltages
V
IntARFF
and
V
IntAGND
for the A/D converter itself.
The SFR DAPR (see figure 7-29) is provided for programming the internal reference voltages
V
IntAREF
and
V
lntAGND
. For this purpose the internal reference voltages can be programmed in steps of
1/16 of the external reference voltages (
V
AREF
–
V
AGND
) by four bits each in register DAPR. Bits 0 to
3 specify
V
lntAGND
, while bits 4 to 7 specify
V
IntAREF
. A minimum of 1 V difference is required between
the internal reference voltages
V
lntARF
and
V
IntAGND
for proper operation of the A/D converter. This
means, for example, in the case where
V
AREF
is 5 V and
V
AGND
is 0 V, there must be at least four
steps difference between the internal reference voltages
V
IntAREF
and
V
IntAGND
.
The values of
V
IntAGND
and
V
IntAREF
are given by the formulas:
DAPR (.3-.0) is the contents of the low-order nibble, and DAPR (.7-.4) the contents of the high-order
nibble of DAPR.
V
IntAGND
=
V
AGND
+
DAPR (.3-.0)
16
(
V
AREF
–
V
AGND
)
with DAPR (.3-.0) < CH;
V
IntAREF
=
V
AGND
+
DAPR (.7-.4)
16
(
V
AREF
–
V
AGND
)
with DAPR (.7-.4) > 3H;
*
Summary of Contents for SAB 80515 Series
Page 9: ...Semiconductor Group 9 Introduction Figure 1 2 Block Diagram ...
Page 12: ...Semiconductor Group 12 Fundamental Structure Figure 2 1 Detailed Block Diagram ...
Page 18: ...Semiconductor Group 18 Central Processing Unit Figure 3 1 Fetch Execute Sequence ...
Page 73: ...Semiconductor Group 73 On Chip Peripheral Components Figure 7 25 A D Converter Block Diagram ...
Page 83: ...Semiconductor Group 83 On Chip Peripheral Components Figure 7 33 a Timer 2 Block Diagram ...
Page 215: ...Device Specifications Semiconductor Group 215 ...
Page 217: ...Device Specifications Semiconductor Group 217 Pin Configuration P LCC 68 ...
Page 219: ...Device Specifications Semiconductor Group 219 Logic Symbol ...
Page 226: ...Device Specifications Semiconductor Group 226 Figure 1 Block Diagram ...
Page 229: ...Device Specifications Semiconductor Group 229 Figure 2 Memory Address Spaces ...
Page 239: ...Device Specifications Semiconductor Group 239 Figure 4 Block Diagram of the A D Converter ...
Page 241: ...Device Specifications Semiconductor Group 241 Figure 5 Interrupt Request Sources ...
Page 242: ...Device Specifications Semiconductor Group 242 Figure 6 Interrupt Priority Level Structure ...