Z8F021ASH020SC datasheet(134/276 Pages) ZILOG

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PS022815-0206

Analog-to-Digital Converter

Z8 Encore! XP® 4K Series

Product Specification

115

can output values across the entire 11-bit range, from -1024 to +1023. In SINGLE-

ENDED mode, the output generally ranges from 0 to +1023, but offset errors can cause

small negative values.

The ADC registers actually return 13 bits of data, but the two LSBs are intended for com-

pensation use only. When the software compensation routine is performed on the 13 bit

raw ADC value, two bits of resolution are lost because of a rounding error. As a result, the

final value is an 11- bit number.

Automatic Powerdown

If the ADC is idle (no conversions in progress) for 160 consecutive system clock cycles,

portions of the ADC are automatically powered down. From this powerdown state, the

ADC requires 40 system clock cycles to power up. The ADC powers up when a conver-

sion is requested by the ADC Control register.

Single-Shot Conversion

When configured for single-shot conversion, the ADC performs a single analog-to-digital

conversion on the selected analog input channel. After completion of the conversion, the

ADC shuts down. The steps for setting up the ADC and initiating a single-shot conversion

are as follows:

1. Enable the desired analog inputs by configuring the general-purpose I/O pins for

alternate analog function. This configuration disables the digital input and output

drivers.

2. Write the ADC High Threshold Register and ADC Low Threshold Register if the

alarm function is required.

3. Write the ADC Control/Status Register 1 to configure the ADC

–

Write to BUFMODE[2:0] to select SINGLE-ENDED or DIFFERENTIAL mode,

as well as unbuffered or buffered mode.

–

If the alarm function is required, set ALMHEN and/or ALMLEN.

–

Write the REFSELH bit of the pair {REFSELH, REFSELL} to select the internal

voltage reference level or to disable the internal reference. The REFSELL bit is.

contained in the ADC Control Register 0.

4. Write to the ADC Control Register 0 to configure the ADC and begin the conversion.

The bit fields in the ADC Control register can be written simultaneously (the ADC

can be configured and enabled with the same write instruction):

–

Write to the ANAIN[3:0] field to select from the available analog input sources

(different input pins available depending on the device)

–

Clear CONT to 0 to select a single-shot conversion.

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