MCP3912 datasheet(47/82 Pages) MICROCHIP

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 2014 Microchip Technology Inc.

DS20005348A-page 47

MCP3912

6.5.2

CONTINUOUS WRITE

The STATUSCOM register contains the write loop

settings for the internal register address pointer

(WRITE). For a continuous write, the address selection

can take the following two values:

SDO is always in a high-impedance state during a

continuous write

communication. Writing

to a

non-writable address (such as addresses 0x00 to

0x07) has no effect and does not increment the

address pointer. In this case, the user needs to stop the

communication and restart a communication with a

control byte pointing to a writable address (0x08 to

0x1F).

6.6

Situations that Reset and Restart

Active ADCs

Immediately after the following actions, the active

ADCs (the ones not in Soft Reset or Shutdown modes)

are reset and automatically restarted in order to provide

proper operation:

Change in PHASE register.

Overwrite of the same PHASE register value.

Change in the OSR<2:0> settings.

Change in the PRE<1:0> settings.

Change in the CLKEXT setting.

Change in the VREFEXT setting.

After these temporary resets, the ADCs go back to

Normal operation, with no need for an additional

command. Each ADC data output register is cleared

during this process. The PHASE register can be used

to serially soft reset the ADCs, without using the

RESET<3:0> bits in the Configuration register, if the

same value is written in the PHASE register.

6.7

Data Ready Pin (DR)

To communicate when channel data is ready for trans-

mission, the data ready signal is available on the Data

Ready pin (DR) at the end of a channel conversion.

The Data Ready pin outputs an active-low pulse with a

pulse width equal to half a DMCLK clock period. After a

data ready pulse falling edge has occurred, the ADC

output data is updated within the tDODR timing and can

then be read through SPI communication.

The first data ready pulse after a Hard or a Soft Reset

is located after the settling time of the sinc filter (see

Table 5-3) plus the phase delay of the corresponding

channel (see Section 5.9 “Phase Delay Block”).

Each subsequent pulse is then periodic, and the period

is equal to a DRCLK clock period (see Equation 4-3

and Figure 1-3). The data ready pulse is always syn-

chronous with the internal DRCLK clock.

The DR pin can be used as an interrupt pin when con-

nected to an MCU or DSP, which will synchronize the

readings of the ADC data outputs. When not active-low,

this pin can either be in high-impedance (when

DR_HIZ = 0) or in a defined logic high state (when

DR_HIZ = 1). This is controlled through the STATUS-

COM register. This allows multiple devices to share the

same Data Ready pin (with a pull-up resistor connected

between DR and DVDD). If only the MCP3912 device is

connected on the interrupt bus, the DR pin does not

require a pull-up resistor, and therefore it is recom-

mended to use DR_HIZ = 1 configuration for such

applications.

The CS pin has no effect over the DR pin, which means

even if the CS pin is logic high, the data ready pulses

coming from the active ADC channels will still be

provided; the DR pin behavior is independent from the

SPI interface. While the RESET pin is logic low, the DR

pin is not active. The DR pin is latched in the logic low

state when the interrupt flag on the CRCREG is present

to signal that the desired registers configuration has

been

corrupted

(see

Section 6.11

“Detecting

Configuration Change Through CRC-16 Checksum

On Register Map and its Associated Interrupt

Flag”

TABLE 6-2:

ADDRESS SELECTION IN

CONTINUOUS WRITE

WRITE

Continuous Read Communications

Static (no incrementation)

Types (default)

Note:

When LOCK<7:0> is different than 0xA5,

all the addresses, except 0x1F, become

nonwritable

(see

Section 4.13

“MCP3912 Delta-Sigma Architecture”

)

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