SAB80C517-M16 SIEMENS [Siemens Semiconductor Group], SAB80C517-M16 Datasheet - Page 86

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

On-Chip Peripheral Components
Ports P7 and P8 are dual purpose input ports. lf the input voltage meets the specified logic levels,
they can be used as digital inputs as well regardless of whether the pin levels are sampled by the
A/D converter at the same time.
The special function register ADDAT (figure 7-28) holds the converted digital 8-bit data result. The
data remains in ADDAT until it is overwritten by the next converted data. ADDAT can be read or
written under software control. lf the A/D converter of the SAB 80C517 is not used, register ADDAT
can be used as an additional general purpose register.
Figure 7-28
Special Function Register ADDAT (Address 0D9 H )
0D9 H
Conversion result
ADDAT
This register contains the 8-bit conversion result.
7.4.1.2 Start of Conversion
An internal start of conversion (ADEX = 0) is triggered by a write-to-DAPR instruction. The start
procedure itself is independent of the value which is written to DAPR. However, the value in DAPR
determines which internal reference voltages are used for the conversion (see section 7.4.2). When
single conversion mode is selected (ADM = 0) only one conversion is performed. In continuous
mode after completion of a conversion a new conversion is triggered automatically, until bit ADM is
reset.
When external start of conversion is selected a write-to-DAPR will not start the conversion; in this
case, conversion starts when a falling edge at pin P6.0/ADST is detected. In single conversion
mode one conversion is performed until the next falling edge at P6.0/ADST is recognized. In
continuous mode new conversions are started automatically as long as pin P6.0/ADST is on low
level. This is done until P6.0/ADST goes to logic high level; in this case the last commenced
conversion is completed.
7.4.2
Reference Voltages
The SAB 80C517 has two pins to which a reference voltage range for the on-chip A/D converter is
V
V
applied (pin
for the upper voltage and pin
for the lower voltage). In contrast to
AREF
AGND
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
and
V
. These steps can individually be assigned as upper and lower reference
AREF
AGND
V
voltage for the converter itself. These internally generated reference voltages are called
and
lNTAREF
V
. The internal reference voltage programming can be thought of as a programmable "D/A
lNTAGND
V
V
converter" which provides the voltages
and
for the A/D converter itself.
INTAREF
INTAGND
Semiconductor Group
87