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UM10360_0
© NXP B.V. 2009. All rights reserved.
User manual
Rev. 00.06 — 5 June 2009
559 of 808
NXP Semiconductors
UM10360
Chapter 30: LPC17xx Digital-to-Analog Converter (DAC)
4.3 D/A Converter Counter Value register (DACCNTVAL - 0x4008 C008)
This read/write register contains the reload value for the Interrupt/DMA counter.
5.
Operation
5.1 DMA counter
When the counter enable bit CNT_ENA in DACCTRL is set, a 16-bit counter will begin
counting down from the value programmed into the DACCNTVAL register. Each time the
counter reaches zero, the counter will be reloaded by the value of DACCNTVAL and the
DMA request bit INT_DMA_REQ will be set in hardware.
Note that the contents of the DACCTRL and DACCNTVAL registers are read and write
accessible, but the timer itself is not accessible for either read or write.
If the DMA_ENA bit is set in the DACCTRL register, the DAC DMA request will be routed
to the GPDMA. When the DMA_ENA bit is cleared, the default state after a reset, DAC
DMA requests are blocked.
Table 522. D/A Control register (DACCTRL - address 0x4008 C004) bit description
Bit
Symbol
Value Description
Reset
Value
0
INT_DMA_REQ 0
This bit is cleared on any write to the DACR register.
0
1
This bit is set by hardware when the timer times out.
1
DBLBUF_ENA
0
DACR double-buffering is disabled.
0
1
When this bit and the CNT_ENA bit are both set, the
double-buffering feature in the DACR register will be
enabled. Writes to the DACR register are written to a
pre-buffer and then transferred to the DACR on the next
time-out of the counter.
2
CNT_ENA
0
Time-out counter operation is disabled.
0
1
Time-out counter operation is enabled.
3
DMA_ENA
0
DMA access is disabled.
0
1
DMA Burst Request Input 7 is enabled for the DAC (see
).
31:4
-
Reserved, user software should not write ones to
reserved bits. The value read from a reserved bit is not
defined.
NA
Table 523: D/A Converter register (DACR - address 0x4008 C000) bit description
Bit
Symbol Description
Reset
Value
15:0
VALUE
16-bit reload value for the DAC interrupt/DMA timer.
0