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XRM(2)-DAC-D4/1G User Guide
V2.2 - Mar 8, 2018
Burst mode is used to extend the reptition rates achievable by means of a 16-bit count register
C, where C is the
count of repetitions of the ARB length
L (the RAM end address). When Burst mode is enabled, the L samples
from the RAM are read out; these are then followed by
{ (C-1)*L} DAC sample clocks of zero-value samples; this
entire sequence is then repeated.
The ARB can also output a digital gate signal ("tick"), synchronous with the data read from RAM, for use with
external hardware. The rising edge of this signal occurs at the start of the burst; the width can be specified to be
a fixed number of FABRCLK cycles up to the length
L of the signal in the RAM using the tick width register.
The TRIG and AUX hardware I/O ports can output this tick by first setting the multiplexer bit to select the tick
signal as the drive source for the AUX or TRIG signal and also configuring the TRIG and/or AUX ports as
outputs. The ARB tick for the I channel is available on the TRIG port whilst that for the Q channel is available on
the AUX port
3.3.6 Self Test Pattern
The DAC provides a pattern testing mode where what is received on the data inputs is compared to the expected
pattern of 0xAAAA/0x5555 and the result of this comparison soignalled via a status bit.
The FPGA must uses two 32-bit registers on each channel to implement this, with the two registers providing the
four consecutive sample values required on each FABRCLK cycle.
Having two programmable registers allows the test pattern to be varied, allowing individual bits to be tested.
3.3.7 Sine Test
A simple 8-sample sine wave can be forced to be the signal source driving the DACs for test and diagnostic
purposes using a single bit.
Page 25
VHDL Structure
xrm-dac-d4-1g-manual_v2_2.pdf