Texas Instruments DAC8881, User Manual, Page: 21 / 25

Using the DAC8881EVM with DXP
www.ti.com
4.4 DAC Output Update Options
The DXP software also allows the user to choose several DAC output update options. These are shown in
Figure 14 .
Figure 14. DAC Output Update Options
Details on these options are shown in Table 9 .
Table 9. Output Update Features
Options Detailed Description
Frame Sync The DXP software defaults to Frame Sync. In this mode, the LDAC pin is held low and the DAC latch is
transparent. The DAC output changes to the corresponding level simultaneously when the DAC latch is
updated. Place a shunt jumper on J1 covering pins 1-2. W10 should be open.
Latch with DSP Jumper W10 on the EVM controls LDAC selection. In this configuration, a timer function on the MMB0
Timer applies a pulse to the LDAC pin and the output of the DAC8881 is updated synchronously with the falling
edge of the applied pulse. Remove the shunt jumper from J1 pins 1-2 and place it on W10 pins 2-3 to use
this feature.
Latch with External Jumper W10, when moved to pins 1-2, routes the LDAC input to pin 15 of J2. This feature allows the user to
Timer apply an LDAC input from an external source. In this mode, J2 pin 15 provides an interrupt to the DSP on
the MMB0 which transfers data from the serial interface to the DAC8881. The LDAC input requirements
must be in accordance with the Timing Characteristics and voltage level inputs found in the device
datasheet.
Update Rate User Input – enter the desired DAC update rate, 1MSPS is the default.
4.5 Data Input Format
The data input format can be configured for either straight binary or binary two’s compliment as shown in
Figure 15 .
Figure 15. Data Format Options
Options Detailed Description
Two's To provide the DAC8881 with two's complement data, the user must install a jumper on J1 pins 7-8. This
Complement grounds the USB/BTC input pin of the DAC8881.
Straight Binary Default state of both DXP and the EVM. In this mode, straight binary data is supplied through the DXP software
to the DAC8881. Ensure there is not jumper loaded at J1 pins 7-8 to use this feature.
20 DAC8881 Evaluation Module SLAU257A – September 2008 – Revised November 2009
Submit Documentation Feedback
Copyright © 2008–2009, Texas Instruments Incorporated