Rainbow-electronics ADC12041 Manual do Utilizador descarregar pdf (Página 24)

Features and Operating Modes (Continued)

SYNC-IN/Synchronous

For the SYNC-IN case, it is assumed that a series of SYNC

pulses at the desired sampling rate are applied at the SYNC

pin of the ADC12041.

8-bit mode: A write to the ADC12041 should set the SYNC

bit, write the START command and clear the BW bit. The

programmed acquisition time in bits b

and b

is a don’t

care condition in the SYNC-IN mode.

A rising edge on the SYNC pin or the second rising edge of

two consecutive reads from the ADC12041 will force the

RDY

signal high. It is recommended that the action of read-

ing from the ADC12041 (not the rising edge of the SYNC

signal) be used to raise the RDY

signal. This will ensure that

the conversion result is read during the acquisition period of

the next conversion cycle, eliminating a read from the

ADC12041 while it is performing a conversion. Noise gener-

ated by accessing the ADC12041 while it is converting may

degrade the conversion result. In the SYNC-IN mode, only

the rising edge of the SYNC signal will begin a conversion

cycle. The rising edge of the SYNC also ends the acquisi-

tion period. The acquisition period begins after the falling

edge of the RDY signal. The input is sampled until the rising

edge of the SYNC pulse, at which time the signal will be

held and conversion begins. The RDY

signal will go low

when the conversion is done and a new operational com-

mand may be written into the Configuration register at this

time, if needed. Two consecutive read cycles are required to

retrieve the entire 13-bit conversion result from the

ADC12041’s Data register. The first read will place the low-

er byte of the conversion result contained in the Data regis-

ter on the data bus. The second read will place the upper

byte of the conversion result stored in the Data register on

the data bus. With the START command in the configuration

the RDY

signal high and begin a conversion cycle following

a rising edge on the SYNC pin.

13-bit mode:

The SYNC bit and the BW bit should be set

and the START command issued with a write to the

ADC12041. A rising edge on the SYNC pin or on the RD pin

will force the RDY

signal high. It is recommended that the

action of reading from the ADC12041 (not the rising edge of

the SYNC signal) be used to raise the RDY

signal. This will

ensure that the conversion result is read during the acquisi-

tion period of the next conversion cycle, eliminating a read

from the ADC12041 while it is performing a conversion.

Noise generated by accessing the ADC12041 while it is

converting may degrade the conversion result. In the SYNC-

IN mode, only the rising edge of the SYNC signal will begin

a conversion cycle. The RDY

signal will go low when the

conversion cycle is done. The acquisition time is controlled

by the SYNC signal. The acquisition period begins after the

falling edge of the RDY

signal. The input is sampled until the

rising edge of the SYNC pulse, at which time the signal will

be held and conversion begins. The RDY

signal will go low

when the conversion is done and a new operational com-

mand may be written into the Configuration register at this

time, if needed. With the START command in the Configura-

tion register, a read from the ADC12041 will place the entire

conversion result stored in the Data register on the data bus

and the rising edge of the read pulse will force the RDY

signal high.

STANDBY COMMAND

8-bit mode:

A write to the ADC12041 should clear the BW

bit and issue the Standby command.

13-bit mode:

A write to the ADC12041 should set the BW bit

and issue the Standby command.

RESET

The RESET command places the ADC12041 into a ready

state and forces the RDY

signal low. The RESET command

can be used to interrupt the ADC12041 while it is performing

a conversion, full-calibration or auto-zero cycle. It can also

be used to get the ADC12041 out of the standby mode.

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