User`s guide

Operation Theorem  35

4.1.3 A/D Trigger Sources Control

The A/D conversion is started by trigger signal. There are total three trigger

sources in the ACL-8316. One is

External trigger source and two are Internal

trigger sources.

The trigger source is programmable by the A/D mode control register.

Please refer to section 3.7 for details of the register. The different trigger

conditions are specified as following:

Software trigger (EXTINT=0, ITSSEL=0)

The trigger source is generated and fully controlled by software under this

mode. That is, the A/D conversion is started by reading the software trigger

applications. However, it is difficult to control the fixed A/D conversion rate

except generating trigger in a timer interrupt service routine with a fixed

trigger rate.

Timer Pacer Trigger (EXTINT=0, ITSSEL=1)

An on-board timer / counter chip 8254 is used to provide an internal trigger

source for A/D conversion at a fixed rate. Two counters of the 8254 chip are

cascaded together to generate trigger pulse with precise period. Please refer

to section 3.4 for 8254 architecture. This mode is ideal for high speed A/D

conversion. It's recommend to use this mode if your applications need a

fixed and precise A/D sampling rate.

External Trigger (EXTINT=1)

Through the pin-17 of CN3 (ExtTrig), the A/D conversion is triggered when a

rising edge of external signal is occurred. The conversion rate under this

mode is more flexible than the previous two modes, because the users can

handle the external signal by outside devices. The external trigger can

combine with the DMA transfer, interrupt data transfer, or even program

polling data transfer. Generally, the interrupt data transfer is more often used

when external trigger mode is used.