JP8 Select External Trigger
Mode Select Trigger Type
Transfer Type
D2 D1 D0 External
Trigger
Software Interrupt DMA
0 0 0 X
X
X
X
0 0 1 X
X
X
X
0 1 0 Select
X
X
Select
1 1 0 Select
Select Select X
The A/D conversion operation can be divided into 2 stages,
trigger stage and transfer
stage
. The trigger stage will generate a trigger signal to A/D converter and the transfer stage
will transfer the result to the CPU.
The trigger method may be
internal trigger
or
external trigger.
The internal trigger can
be
software trigger
or
pacer trigger.
The software trigger is very simple but can not
control the sampling rate very precisely.
In software trigger mode, the program issues a
software trigger command any time needed. Then the program will poll the A/D status bit
until the ready bit is 0.
The pacer trigger can control the sampling rate very precisely. So the converted
data can be used to reconstruct the waveform of analog input signal
. In pacer trigger
mode, the pacer timer will generate trigger signals to A/D converter periodic. These
converted data can be transfer to the CPU by polling or interrupt or DMA transfer method.
The software driver provides three data transfer methods,
polling, interrupt and DMA.
The polling subroutine, A-812PG_AD_PollingVar() or A-812PG_AD_PollingArray(), set
A/D mode control register to
0x01.
This control word means software trigger and polling
transfer. The interrupt subroutine, A-812PG_AD_INT_START(…), set A/D mode control
mode register to
ox06.
This control word means pacer trigger and interrupt transfer. The
DMA subroutine, A-812PG_AD_DMA_START(…), set A/D mode control register to
0x02
.
This control word means pacer trigger and DMA transfer.
A-812PG Hardware Manual (Ver.1.2, Sep/2005, IPH-004-12) -----
22