Xtreme I/O Express ADC-DAC
Users Guide
Document: CTIM-00435
Revision: 0.08
Page 20 of 47
Connect Tech Inc. 800-426-8979 | 519-836-1291
Date: 2016-11-18
Analog Outputs (DAC’s)
Overview
The
Xtreme I/O Express ADC-DAC
uses a 16-bit 4-channel DAC IC which is interfaced to the on-
board FPGA. The DAC IC datasheet can be found here:
http://www.ti.com/lit/gpn/dac8734
Connectors & Jumpers
Function Analog Inputs
Location P7
Type
Samtec TSW-105-08-L-D-RA
2x5, 0.100” pitch
Mate
Any 0.100” cable
Pinout
Pin Description Pin Description
1
DAC_OUTA 2
GND
3
DAC_OUTB 4
GND
5
DAC_OUTC 6
GND
7
DAC_OUTD 8
GND
9
GND
10
GND
Operation
The DAC8734 IC has 4 DAC outputs Channel 0,1,2 and 3. The DAC block can be configured to
drive the DAC peripheral from one of three sources, direct software writes (
Direct Write Mode
),
block ram stored sequences (
Signal Gen Mode
) or a built in PWM (
PWM Mode
). On power on the
DAC defaults to the first mode but can easily be switched to one of the other two by writing to the
appropriate bits in the TRG_SIGGEN_PWM register.
Direct Write Mode
In this mode the DAC controller responds to writes to the CH0_DATA, CH1_DATA, CH2_DATA,
CH3_DATA registers and then immediately sends the contents of one or the other if it detects a write
has been made. A write to CH0_DATA will trigger the transmission of the new values to channel 0
and 1 and a write to address CH2_DATA will trigger the transmission of the new values to channel 2
and channel 3.
While the controller will always send in two channel values at a time, one can use byte enables to
write just 16 bits to either the upper or lower portion of one of the Direct Write Mode data registers.
When the transmission to the peripheral is then triggered the old value in the other channel slot will be
rewritten with the same thing.
Signal Gen Mode
The purpose of this mode is to allow the board to generate arbitrary, user-defined signals through the
DAC peripheral independent of any active software management. When operating in this capacity,
the board will persistently source its outputs to the DAC peripheral from values stored in its
associated block memory in a manner as dictated by the fields within the
SIG_GEN_RD_CTRL