Omega OME-A822PG manual 1 A/D conversion flow, Polling, interrupt and DMA

2.7.1 A/D conversion flow

Before using the A/D converter, the user should configure the following hardware settings:

1.select single-ended or differential input (JP3) (refer to Sec. 2.9 first)

2.select internal trigger or external trigger (JP4)

3.select IRQ level if needed (JP5)

4.select DMA channel if needed (JP7,JP8)

5.select internal clock or external clock for counter0 if needed (JP6)

The user must decide which A/D conversion mode will be used. The software driver supports three different modes: polling, interrupt and DMA. The polling mode (sec. 2.4.9) is the simplest but most limited. The software driver should be used for interrupt or DMA mode.

The analog input signals come from CN3. These signals may be single-ended or differential and must match the setting of JP3.

The multiplexer can select 16 single-ended or 8 differential signals into the gain control module. The settling time of multiplexer depends on the source resistance. Because the software doesn’t account for the settling time, the user should provide sufficient delay when switching channels. (sec. 2.4.7)

The gain control module also requires settling time if the gain control code is changed.

Since the software doesn’t account for settling time, the user should provide sufficient delay if the gain control code is changed. (sec. 2.4.6)

The software driver provides a machine independent timer, A-822_Delay(), for settling time delay. This subroutine assumes that the JP6 jumper is set to the internal 2M clock and uses counter0 to implement a machine independent timer. If A-822_Delay() is used, counter0 will be reserved and can not be used as a user programmable timer/counter.

The A/D converter needs a trigger signal to start an A/D conversion cycle. The OME-A-822PGL/PGH supports three trigger modes, software, pacer and external trigger.

The result of the A/D conversion can be transferred into the PC memory by three modes:

polling, interrupt and DMA..

OME-A-822PGL/PGH Hardware Manual ---- 28