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CY8C28xxx PSoC Programmable System-on-Chip TRM, Document No. 001-52594 Rev. *G
Two Column Limited Analog System
24.1.1.1
Analog Comparator Bus Interface
Each analog column has a dedicated comparator bus asso-
ciated with it. In the CY8C28xxx, PSoC devices, only the
Continuous Time (CT) block can drive this bus. The output
on the comparator bus cannot drive into the digital blocks as
a data input. It can serve as an input to Switched Capacitor
(SC) blocks as an interrupt input, and is available as read
only data in the Analog Comparator Control register
(ACE_CMP_CR0). It can be driven to the global output bus
by way of the Comparator to Global Input Enable register
(ACE_CMP_GI_EN).
illustrates one column of the comparator bus.
The comparator bus is synchronized by the selected column
clock before it is available, to either drive the digital blocks,
interrupt, SC blocks, or for it to be read in the
ACE_CMP_CR0 register. There is also an option to bypass
the synchronization in each column into a transparent mode
by setting bits in the ACE_CMP_CR1 register.
As shown in
, the comparator bus output is gated
by the primary output of a selected digital block. This feature
is used to precisely control the conversion period of a single
slope ADC. Any digital block can be used to drive the gate
signal. This selection may be made with the ICLKS bits in
registers DEC_CR0 and DEC_CR1. This function may be
enabled on a column-by-column basis, by setting the
ACE_IGEN bits in the DEC_CR0 register. Alternately, the
dedicated ADC PWM, with VC3 as input, can be used to
gate the ADC conversion period without the need for a digi-
tal block. When this dedicated PWM is configured, it over-
rides the ICLKS selection as defined by the DEC_CR0 and
DEC_CR1 registers.
The analog comparator bus output values can be modified
or combined with another analog comparator bus through
the Analog Look-Up-Table (LUT) function. The LUT takes
two inputs, A and B, and provides a selection of 16 possible
logic functions for those inputs. The LUT A and B inputs for
each column comparator output is shown in the following
table.
The LUT configuration is set in two control registers,
ACE_ALT_CR0 and ACE_ALT_CR1. Each selection for
each column is encoded in four bits. The function value cor-
responding to the bit encoding is shown in
24.1.1.2
Analog Column Clock Generation
The input clock source for each column clock generator is
selectable according to the ACE_CLK_CR0 register. There
are four selections for each column: VC1, VC2, ACLK4, and
ACLK5. An additional selection, SYSCLK, is controlled by
the ACE_CLK_CR3 register. The VC1 and VC2 clock sig-
nals are global system clocks. Programming options for
these system clocks can be accessed in the OSC_CR1 reg-
ister. Each of the ACLK4 and ACLK5 clock selections are
driven by a selection of digital block outputs. The settings for
the digital block selection are located in the ACE_CLK_CR1
register. The ACE_CLK_CR3 register has additional column
clock options. This register allows for a direct SYSCLK
option as well as the option to divide the selected column
clock by 2, 4, or 8.
24.1.1.3
Single Slope ADC
A simplified block diagram of the single slope ADC (SSADC)
implementation is show in
. The core of the con-
version algorithm involves a current source, an integrating
capacitor, and a comparator. When the current source is
activated, a linear voltage ramp is generated on the capaci-
tor. This voltage is an input to an analog comparator circuit;
the other input of which is the analog input voltage to be
converted. With the polarity of hookup as shown, the com-
parator will be high until the ramp voltage equals the input
voltage, at which time it will transition low. A counter gate is
generated by the AND of the PWM high time (which defines
the start of the ramp) and the comparator (which defines the
trip point or the end of the conversion for a given voltage).
When the conversion is complete, the code may be read
from the counter. Each column has an ADC configuration
register (ACE_ADCx_CR).
Table 24-1. A and B Inputs for Each Column Comparator
LUT Output for the CY8C28xxx Devices
Comparator
LUT Output
A
B
Column 4
ACMP4
ACMP5
Column 5
ACMP5
0
Table 24-2. RDIxLTx Register
LUTx[3:0]
0h: 0000: FALSE
1h: 0001: A .AND. B
2h: 0010: A .AND. B
3h: 0011: A
4h: 0100: A .AND. B
5h: 0101: B
6h: 0110: A .XOR. B
7h: 0111: A .OR. B
8h: 1000: A .NOR. B
9h: 1001: A .XNOR. B
Ah: 1010: B
Bh: 1011: A .OR. B
Ch: 1100: A
Dh: 1101: A .OR. B
Eh: 1110: A. NAND. B
Fh: 1111: TRUE
Summary of Contents for CY8C28 series
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