Datasheet

Data Sheet ADuC7124/ADuC7126
Rev. C | Page 43 of 108
TEMPREF Register
Name: TEMPREF
Address: 0xFFFF0548
Default Value: 0xXXXX
Access: Read/write
Table 35. TEMPREF MMR Bit Descriptions
Bit Description
[15:9] Reserved.
8 Temperature reference voltage sign bit.
[7:0] Temperature sensor offset calibration voltage.
To calculate the V
TEMP
from the TEMPREF register,
perform the following calculation:
If TEMPREF sign is negative,
C
TREF
= 2292 − TEMPREF[7:0]
where TEMPREF[8] = 1
Or
If TEMPREF sign is positive,
C
TREF
= TEMPREF[7:0] + 2292
where TEMPREF[8] = 0.
Finally,
V
TREF
= ((C
TREF
× V
REF
)/4096) × 1000
Insert V
TREF
into
T − T
REF
= (V
ADC
− V
TREF
) × K
Note that the ADC Code Value 2292 is a default value
when using the TEMPREF register. It is not an exact
value and must only be used with the TEMPREF
register.
BAND GAP REFERENCE
Each ADuC7124/ADuC7126 provides on-chip band gap
references of 2.5 V, which can be used for the ADC and DAC.
This internal reference also appears on the V
REF
pin. When using
the internal reference, a 0.47 µF capacitor must be connected from
the external V
REF
pin to AGND to ensure stability and fast
response during ADC conversions. This reference can also be
connected to an external pin (V
REF
) and used as a reference
for other circuits in the system. An external buffer is required
because of the low drive capability of the VREF output (<5 µA).
A programmable option also allows an external reference input
on the V
REF
pin. Note that it is not possible to disable the
internal reference. Therefore, the external reference source must
be capable of overdriving the internal reference source.
REFCON Register
Name: REFCON
Address: 0xFFFF048C
Default Value: 0x00
Access: Read/write
The band gap reference interface consists of an 8-bit MMR
REFCON, described in Table 36.
Table 36. REFCON MMR Bit Descriptions
Bit Description
[7:2] Reserved.
1 Internal reference power-down bit.
Set this bit to 1 to power down the internal reference
source. This bit should be set when connecting an
external reference source.
Clear this bit to enable the internal reference.
This bit is cleared by default.
0 Internal reference output enable.
Set by the user to connect the internal 2.5 V reference
to the V
REF
pin. The reference can be used for an
external component but must be buffered.
Cleared by the user to disconnect the reference from
the V
REF
pin.
To connect an external reference source to the ADuC7124/
ADuC7126, configure REFCON = 0x00. ADC and the DACs
can be configured to use same or a different reference resource
(see Table 66).