TMP320C2811PBKA datasheet(59/147 Pages) TI

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Peripherals

June 2004

SPRS257

Result Registers

EVB

S/W

ADCSOC

EVA

S/W

Sequencer 2

Sequencer 1

SOC

ADC Control Registers

70B7h

70B0h

70AFh

70A8h

Result Reg 15

Result Reg 8

Result Reg 7

Result Reg 1

Result Reg 0

Module

ADC

12-Bit

Analog

MUX

ADCINA0

ADCINA7

ADCINB0

ADCINB7

System

Control Block

High-Speed

Prescaler

HSPCLK

ADCENCLK

C28x

SYSCLKOUT

S/H

Figure 4−4. Block Diagram of the R281x ADC Module

To obtain the specified accuracy of the ADC, proper board layout is very critical. To the best extent possible,

traces leading to the ADCIN pins should not run in close proximity to the digital signal paths. This is to minimize

switching noise on the digital lines from getting coupled to the ADC inputs. Furthermore, proper isolation

techniques must be used to isolate the ADC module power pins (VDDA1/VDDA2, AVDDREFBG) from the digital

supply. Figure 4−5 shows the ADC pin connections for R281x devices.

Notes:

1. The ADC registers are accessed at the SYSCLKOUT rate. The internal timing of the ADC module is

controlled by the high-speed peripheral clock (HSPCLK).

2. The behavior of the ADC module based on the state of the ADCENCLK and HALT signals is as follows:

ADCENCLK: On reset, this signal will be low. While reset is active-low (XRS) the clock to the register will

still function. This is necessary to make sure all registers and modes go into their default reset state. The

analog module will however be in a low-power inactive state. As soon as reset goes high, then the clock to

the registers will be disabled. When the user sets the ADCENCLK signal high, then the clocks to the

registers will be enabled and the analog module will be enabled. There will be a certain time delay (ms

range) before the ADC is stable and can be used.

HALT: This signal only affects the analog module. It does not affect the registers. If low, the ADC module is

powered. If high, the ADC module goes into low-power mode. The HALT mode will stop the clock to the

CPU, which will stop the HSPCLK. Therefore the ADC register logic will be turned off indirectly.

Figure 4−5 shows the ADC pin-biasing for internal reference and Figure 4−6 shows the ADC pin-biasing for

external reference.

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