ADUC7028 Analog Devices, ADUC7028 Datasheet - Page 53

• Manufacturer Part Number: ADUC7028
• Manufacturer: Analog Devices

Specifications of ADUC7028

• Mcu Core: ARM7 TDMI
• Mcu Speed (mips): 40
• Flash (kbytes): 62Bytes
• Sram (bytes): 8192Bytes
• Gpio Pins: 40
• Adc # Channels: 8

Linearity degradation near ground and AV
ration of the output amplifier, and a general representation of its
effects (neglecting offset and gain error) is illustrated in Figure 54.
The dotted line in Figure 54 indicates the ideal transfer function,
and the solid line represents what the transfer function may
look like with endpoint nonlinearities due to saturation of the
output amplifier. Note that Figure 54 represents a transfer function
in 0-to-AV
(with V
similar. However, the upper portion of the transfer function
follows the ideal line right to the end (V
showing no signs of endpoint linearity errors.
The endpoint nonlinearities conceptually illustrated in
Figure 54 get worse as a function of output loading. Most
of the ADuC7019/20/21/22/24/25/26/27/28/29 data sheet
specifications assume a 5 kΩ resistive load to ground at the
DAC output. As the output is forced to source or sink more
current, the nonlinear regions at the top or bottom (respectively)
of Figure 54 become larger. With larger current demands, this
can significantly limit output voltage swing.
POWER SUPPLY MONITOR
The power supply monitor regulates the IOV
ADuC7019/20/21/22/24/25/26/27/28/29. It indicates when the
IOV
The monitor function is controlled via the PSMCON register.
If enabled in the IRQEN or FIQEN register, the monitor
interrupts the core using the PSMI bit in the PSMCON MMR.
This bit is immediately cleared after CMP goes high.
This monitor function allows the user to save working registers
to avoid possible data loss due to low supply or brown-out
conditions. It also ensures that normal code execution does not
resume until a safe supply level is established.
Table 53. PSMCON Register
Name
PSMCON
DD
Figure 54. Endpoint Nonlinearities Due to Amplifier Saturation
AV
supply pin drops below one of two supply trip points.
REF
DD
< AV
DD
– 100mV
100mV
mode only. In 0-to-V
AV
Address
0xFFFF0440
DD
DD
or DAC
0x00000000
REF
< AV
Default Value
0x0008
REF
DD
), the lower nonlinearity is
REF
or 0-to-DAC
in this case, not AV
DD
DD
is caused by satu-
0x0FFF0000
supply on the
REF
mode
Access
R/W
DD
Rev. D | Page 53 of 96
),
Table 54. PSMCON MMR Bit Descriptions
Bit
3
2
1
0
COMPARATOR
The ADuC7019/20/21/22/24/25/26/27/28/29 integrate voltage
comparators. The positive input is multiplexed with ADC2, and
the negative input has two options: ADC3 and DAC0. The output
of the comparator can be configured to generate a system inter-
rupt, be routed directly to the programmable logic array, start
an ADC conversion, or be on an external pin, CMP
shown in Figure 55.
Note that because the ADuC7022, ADuC7025, and ADu7027
parts do not support a DAC0 output, it is not possible to use
DAC0 as a comparator input on these parts.
Hysteresis
Figure 56 shows how the input offset voltage and hysteresis
terms are defined.
ADuC7019/20/21/22/24/25/26/27/28/29
Name
CMP
TP
PSMEN
PSMI
P0.0/CMP
ADC2/CMP0
ADC3/CMP1
Figure 56. Comparator Hysteresis Transfer Function
CMP
OUT
Description
Comparator bit. This is a read-only bit that
directly reflects the state of the comparator.
Read 1 indicates that the IOV
its selected trip point or that the PSM is in
power-down mode. Read 0 indicates that the
IOV
bit should be set before leaving the interrupt
service routine.
Trip point selection bit. 0 = 2.79 V, 1 = 3.07 V.
Power supply monitor enable bit. Set to 1 to
enable the power supply monitor circuit. Cleared
to 0 to disable the power supply monitor circuit.
Power supply monitor interrupt bit. This bit is set
high by the MicroConverter after CMP goes low,
indicating low I/O supply. The PSMI bit can be
used to interrupt the processor. After CMP
returns high, the PSMI bit can be cleared by
writing a 1 to this location. A 0 write has no
effect. There is no timeout delay; PSMI can be
immediately cleared after CMP goes high.
OUT
DD
DAC0
supply is below its selected trip point. This
V
Figure 55. Comparator
OS
V
H
MUX
V
H
CMP0
DD
MUX
supply is above
OUT
IRQ
, as