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CY8C28xxx PSoC Programmable System-on-Chip TRM, Document No. 001-52594 Rev. *G
Analog Reference
21.2
Register Definitions
The following register is associated with the Analog Reference. For a complete table of all analog registers, refer to the
mary Table of the Analog Registers” on page 389
The register description below has an associated register table showing the bit structure. Depending on how many analog col-
umns your PSoC device has (see the Cols. column in the register tables below), only certain bits are accessible to be read or
written. The bits that are grayed out throughout this manual are reserved bits and are not detailed in the register description
that follows. Reserved bits should always be written with a value of ‘0’.
21.2.1
ARF_CR Register
The Analog Reference Control Register (ARF_CR) is used
to configure various features of the configurable analog ref-
erences.
This register can only be used with four and two column
PSoC devices.
Note
The external bypass capacitor bit 6 (AGNDBYP) in the
Bandgap Trim register (BDG_TR: 1, EAh) controls the exter-
nal bypass capacitor. The default value is zero, which dis-
ables this function (see
). The figure shows the
two switches in the AGND path in their default state. If bit 6
is set, then the P2[4] I/O should be tri-stated and an external
capacitor connect from P2[4] to Vss.
Bit 6: HBE.
This bit controls the
level for all the
opamps. It operates with the power setting in each block, to
set the parameters of that block. Most applications will bene-
fit from the low bias level. At high bias, the analog block
opamps have a faster slew rate, but slightly less voltage
swing and higher power.
Bits 5 to 3: REF[2:0].
REF (AGND, RefHI, and RefLO)
sets the analog array reference control, selecting specific
combinations of voltage for analog ground and references.
Many of these reference voltages are based on the preci-
sion internal reference, a silicon bandgap operating at 1.30
volts. This reference has good thermal stability and power
supply rejection.
Alternatively, the power supply can be scaled to provide
analog ground and references; this is particularly useful for
signals which are ratiometric to the power supply voltage.
See
User supplied external precision references can be con-
nected to Port 2 inputs (available on 28 pin and larger parts).
This is useful in setting reference for specific customer appli-
cations, such as a ±1.00 V (from AGND) ADC scale. Refer-
ences derived from Port 2 inputs are limited to the same
output voltage range as the opamps in the analog blocks.
Note that only the 010b setting for REF[2:0] is valid in the
one column PSoC device. This sets AGND = Vdd/2,
RefHi = Vdd, and RefLo = Vss.
Bits 2 to 0: PWR[2:0].
PWR controls the bias current and
bandwidth for all of the opamps in the analog reference
block. PWR also provides on/off control in various rows of
the analog array.
For additional information, refer to the
.
Add.
Name
Cols.
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
Access
0,63h
4, 2
HBE
REF[2:0]
PWR[2:0]
RW : 00
Table 21-1. Analog Array Power Control Bits
PWR[2:0]
CT Row
Both SC Rows
REF Bias
000b
Off
Off
Off
001b
On
Off
Low
010b
On
Off
Medium
011b
On
Off
High
100b
Off
Off
Off
101b
On
On
Low
110b
On
On
Medium
111b
On
On
High
Содержание CY8C28 series
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