Xilinx XAPP169 - Manual (Page 24)

24 www.xilinx.com XAPP169 (v1.0) November 24, 1999
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MP3 NG: A Next Generation Consumer Platform R
Like the IRDA controller, an interrupt is generated every time the FIFOs transfer their last word
into the shift registers. Assuming a 48 kHz audio sampling rate, this will result in an interrupt
every 83.3
µ
s. To put this in perspective, this means that the CPU will get an interrupt every
5,333 instructions.
Touch Screen Interface
The touch screen interface is an I/O port that lets the processor read the data returned by a
two-channel analog-to-digital converter. This lets the system software read the X and Y
coordinate resistance values that result from the user touching the screen. The system
software handles linearization and filters out transient touch events. (See
Figure 23 and
Table 7 .)
Table 6: Audio DAC Interface Signal Summary
Signal Type Description
DAC_MCLK Output Master clock
DAC_LRCK Output Left / Right clock, determines which channel is currently being
transferred
DAC_SDATA Output Serial audio data
DAC_SCL Output I
2
C data clock
DAC_SDA I/O I
2
C data
Table 7: Touch Screen Interface Signal Summary
Signal Type Description
AD_SCK Output Serial data clock
AD_SDI Input Serial data in
AD_SDO Output Serial data out
Register
D Q D_IN[31:0]
32 3
AD_SCK
AD_SDO
D_OUT[31:0]
32
AD_SDI
Figure 23: Touch Interface Block Diagram