Data Transfer from ADC to DAC (Passthrough)

The left-aligned 8-bit ADC result in ADRESH register can be transferred directly to the DAC using DMA, creating an audio pass-through channel⁽¹⁾. The DMA setup configurations are listed in Table 3-6.

Table 1. DMA Setup Configuration (DMA1)
DMA1 Setup
SSA	Source Address	&ADRESH
SSZ	Source Size	1
SMR	Source Memory Region	SFR
SMODE	Source Address Mode	SPTR remains unchanged
DSA	Destination Address	&DAC1DATL
DSZ	Destination Size	1
DMODE	Destination Address Mode	DPTR remains unchanged
SIRQEN	Start Trigger Enable	Yes
SIRQ	Start Trigger	AD (ADC conversion)
SSTP	Source Counter Reload Stop	No - SIRQEN not cleared
DSTP	Destination Counter Reload Stop	No - SIRQEN not cleared
AIRQEN	Abort Trigger Enable	No (stops when SCNT/DCNT reloads)
AIRQ	Abort Trigger	N/A

How It Works:

1.The DMA is triggered as soon as an ADC conversion is complete (ADIF trigger) and the content of ADRESH register is transferred to the DAC1DATL register directly. Because SSZ = 1, the DMA stops after the first transfer and waits for the next trigger.
2.This process continues as long as the ADC and the DMA are in operation.

Important:

1.While most of the newer PIC18 devices have a 10-bit or 12-bit ADC, only 8-bit ADC values are used to keep the application simple. This is because the DAC used to playback the audio signal has a resolution of 8-bits.