A/D Converter, Temperature Sensor, Programmable Gain
Amplifier, and Stand-Alone Amplifier.
15.0 A/D Converter
This device contains a 7-channel, multiplexed input, succes-
sive approximation, 10-bit Analog-to-Digital Converter with
Programmable Gain Amplifier. One A/D channel is internally
connected to the temperature sensor. The remaining six
channels are connected to pins B2-B7 and are available
external to the device. Pins AVCC and AGND are used for the
15.1 9.1 OPERATING MODES
The simplified block diagram of the A/D Converter is shown
in Figure 25.
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FIGURE 25. Simplified A/D Converter Block Diagram
The A/D Converter supports both Single Ended and Differ-
ential modes of operation. Differential mode is only sup-
ported when the programmable gain amplifier is bypassed.
powered down and the A/D result registers have unknown
data. The offset trim registers are also initialized to 40 Hex
on Reset and need to be re-trimmed, if being used. The gain
register is initialized to 00 on Reset.
Two specific analog channel selection modes are supported.
These are as follows:
15.1.1 A/D Control Register
1. Allow any specific channel, except for the temperature
sensor input, with or without the programmable gain
amplifier, to be selected at one time. The A/D Converter
performs the specific conversion requested and stops.
When using the temperature sensor, the programmable
gain amplifier is required. See the Temperature Sensor
section for more details on using the temperature sen-
sor.
The control register, ENAD contains 4 bits for channel se-
lection, 1 bit for mode selection, 1 bit for the multiplexor
output selection, 1 bit for prescaler selection, and a Busy bit.
An A/D conversion is initiated by setting the ADBSY bit in the
ENAD control register. The result of the conversion is avail-
able to the user in the A/D result registers, ADRSTH and
ADRSTL, when ADBSY is cleared by the hardware on
completion of the conversion.
2. Allow any differential channel pair to be selected at one
time. The A/D Converter performs the specific differen-
tial conversion requested and stops. Differential mode is
only supported when the programmable gain amplifier is
bypassed.
TABLE 21. ENAD Register
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
Channel Select
Mode Mux/Out Prescale Busy
Select
In both Single Ended mode and Differential mode, there is
the capability to connect the analog multiplexor output, with
the exception of the temperature sensor input, and A/D
converter input to external pins. This provides the ability to
externally connect a common filter/signal conditioning circuit
for the A/D Converter.
ADCH3 ADCH2 ADCH1 ADCH0 ADMOD
MUX
PSC
ADBSY
15.1.1.1 Channel Select
This 4-bit field selects one of seven channels to be the VIN+
.
The mode selection and the mux output determine the VIN-
input. When MUX = 0, all seven channels are available, as
shown in Table 22. When MUX = 1, only 4 channels are
available, as shown in Table 23.
The A/D Converter is supported by six memory mapped
registers: two result registers, the control register, two offset
trimming registers, and the gain register. When the device is
reset, the mode control register (ENAD) is cleared, the A/D is
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