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24 www.xilinx.com XAPP169 (v1.0) November 24, 1999
1-800-255-7778
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
µs. 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
DQ
D_IN[31:0]
32
3
AD_SCK
AD_SDO
D_OUT[31:0]
32
AD_SDI
Figure 23: Touch Interface Block Diagram