8.
Toggle START bit to start pacer.
1024 samples or more:
1.
Stop pacer by setting 8254 to mode 2.
2.
Clear FIFO.
3.
Disable and reset interrupts.
4.
Set channel limits.
5.
Set START bit to hold off pacer.
6.
Initialize the 8254.
7.
Load FIFO with first 1024 samples.
8.
Install Interrupt Service Routine (ISR).
9.
Enable interrupts and clear START bit. The DACs will begin updating immediately.
Upon the FIFO becoming half-empty, the board will assert an INT. The ISR is responsible for filling the FIFO with 256 samples on
each interrupt. Upon filling the FIFO with the last of the data, the ISR should disable the interrupts and be un-installed.
CIO-DAC04/12-HS REGISTER MAP
Base + 0 (DAC LSB)
RD -------------------- RESETS INTERRUPT -------------------------------
WR D3 D2 D1 D0 N/A N/A N/A N/A
Base + 1 (DAC MSB)
RD ------------------- RESETS FIFO ------------------------------------------
WR D11 D10 D9 D8 D7 D6 D5 D4
Base + 2 (Channel select)
RD N/A N/A H1 H0 N/A N/A L1 L0
WR N/A N/A H1 H0 N/A N/A L1 L0
This address sets the active D/A channels. The channels selected must be consecutive. This register sets a start channel and a stop
channel. Channels in-between are automatically written to. You cannot jump channels between your start and stop channels. (i.e., if
you start at ch 1 and stop at ch 3, you will also write data to ch 2) The table below describes the start/stop channel selections.
Hi
gh or Stop Channel Low or Start Channel
CH H1 H0 CH L1 L0
000 000
101 101
210 210
311 311
The stop channel must always be greater than or equal to the start channel. For single channel operation, Start Ch. = Stop Ch.
Base + 3 (Control / Status)
RD INTE INT2 INT1 INT0 FFE FFHF FFERR INTST
WR INTE INT2 INT1 INT0 N/A N/A SIMUL START
Control Register Description (Write Base + 3):
Bit #
Name Description
0 START Used when total count is less than 1024. Setting the START bit starts DAC output
process. Since count is less than 1024, no interrupts are required.
= 0 Pacer starts when sample #1024 is written.
= 1 Transfers one sample if 8254 not programmed (Direct mode).
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(18 paginas)
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