SH7261 datasheet(1063/1348 Pages) RENESAS

1063 / 1348 page

Section 22 A/D Converter (ADC)

Rev. 2.00 Sep. 07, 2007 Page 1031 of 1312

REJ09B0320-0200

22.5

Interrupt Sources and DMAC Transfer Request

The A/D converter generates an A/D conversion end interrupt (ADI) at the end of A/D conversion.

An ADI interrupt request is generated if the ADIE bit is set to 1 when the ADF bit in ADCSR is

set to 1 on completion of A/D conversion. Note that the direct memory access controller (DMAC)

can be activated by an ADI interrupt depending on the DMAC setting. In this case, an interrupt is

not issued to the CPU. If the setting to activate the DMAC has not been made, an interrupt request

is sent to the CPU. Having the converted data read by the DMAC in response to an ADI interrupt

enables continuous conversion to be achieved without imposing a load on software.

In single mode, set the DMAC so that DMA transfer initiated by an ADI interrupt is performed

only once. In the case of A/D conversion on multiple channels in scan mode or multi mode, setting

the DMA transfer count to one causes DMA transfer to finish after transferring only one channel

of data. To make the DMAC transfer all conversion data, set the ADDR where A/D conversion

data is stored as the transfer source address, and the number of converted channels as the transfer

count.

When the DMAC is activated by ADI, the ADF bit in ADCSR is automatically cleared to 0 when

data is transferred by the DMAC.

Table 22.6

Relationship between Interrupt Sources and DMAC Transfer Request

Name

Interrupt Source

Interrupt Flag

DMAC Activation

ADI

A/D conversion end

ADF in ADCSR

Possible

22.6

Definitions of A/D Conversion Accuracy

The A/D converter compares an analog value input from an analog input channel with its analog

reference value and converts it to 10-bit digital data. The absolute accuracy of this A/D conversion

is the deviation between the input analog value and the output digital value. It includes the

following errors:

• Offset error

• Full-scale error

• Quantization error

• Nonlinearity error

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