Datasheet

ADuC7060/ADuC7061 Data Sheet
Rev. D | Page 54 of 108
Excitation Current Sources Control Register
Name: IEXCON
Address: 0xFFFF0570
Default value: 0x00
Access: Read and write
Function: This 8-bit MMR controls the two excitation current sources, IEXC0 and IEXC1.
Table 62. IEXCON MMR Bit Designations
Bit Name Description
7 IEXC1_EN Enable bit for IEXC1 current source.
Set this bit to 1 to enable Excitation Current Source 1.
Clear this bit to disable Excitation Current Source 1.
6 IEXC0_EN Enable bit for IEXC0 current source.
Set this bit to 1 to enable Excitation Current Source 0.
Clear this bit to disable Excitation Current Source 0.
5 IEXC1_DIR Set this bit to 1 to direct Excitation Current Source 1 to the IEXC0 pin.
Set this bit to 0 to direct Excitation Current Source 1 to the IEXC1 pin.
4 IEXC0_DIR Set this bit to 1 to direct Excitation Current Source 0 to the IEXC1 pin.
Set this bit to 0 to direct Excitation Current Source 0 to the IEXC0 pin.
3:1 IOUT[3:1] These bits control the excitation current level for each source.
IOUT[3:1] = 000, excitation current = 0 μA + (IOUT[0] × 10 μA).
IOUT[3:1] = 001, excitation current = 200 μA + (IOUT[0] × 10 μA).
IOUT[3:1] = 010, excitation current = 400 μA + (IOUT[0] × 10 μA).
IOUT[3:1] = 011, excitation current = 600 μA + (IOUT[0] × 10 μA).
IOUT[3:1] = 100, excitation current = 800 μA + (IOUT[0] × 10 μA).
IOUT[3:1] = 101, excitation current = 1 mA + (IOUT[0] × 10 μA).
All other values are undefined.
0 IOUT[0] Set this bit to 1 to enable 10 μA diagnostic current source.
Clear this bit to 0 to disable 10 μA diagnostic current source.
EXAMPLE APPLICATION CIRCUITS
Figure 18 shows a simple bridge sensor interface to the
ADuC706x, including the RC filters on the analog input
channels. Notice that the sense lines from the bridge
(connecting to the reference inputs) are wired separately from
the excitation lines (going to DVDD/AVDD and ground). This
results in a total of six wires going to the bridge. This 6-wire
connection scheme is a feature of most off-the-shelf bridge
transducers (such as load cells) that helps to minimize errors
that would otherwise result from wire impedances.
In Figure 19, the AD592 is an external temperature sensor used to
measure the thermocouple cold junction, and its output is con-
nected to the auxiliary channel. The ADR280 is an external 1.2 V
reference part—alternatively, the internal reference can be used.
Here, the thermocouple is connected to the primary ADC as
a differential input to ADC0/ADC1. Note the resistor between
VREF+ and ADC1 to bias the ADC inputs above 100 mV.
Figure 20 shows a simple 4-wire RTD interface circuit. As with
the bridge transducer implementation in Figure 18, if a power
supply and a serial connection to the outside world are added,
Figure 20 represents a complete system.