Texas Instruments ADS1178EVM, Руководство пользователя, Страница: 10 / 52

7.1 Usage in PDK
7.2 Usage as a Stand-Alone EVM
8 EVM Operation
8.1 Analog Input
EVM Operation
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If using the ADS1278EVM as part of the ADS1278EVM-PDK, J19 should not have any pins shorted.
Remove any shorting blocks on jumper J19. The ADS1278EVM-PDK software will allow selection of the
clock source under software control (this is accomplished by using port 05 of the I
2
C expander U17). The
software allows selection of the onboard 27MHz oscillator, or a clock provided by a PLL on the MMB0 that
directly drives the appropriate CLK pins of the interface, or an external, customer-supplied clock. If an
external clock is selected with the software, this clock must be provided on J18. Note that if the external
clock is selected and no clock is provided, the software may hang waiting for data from the converter.
If using the EVM in your own system and not with the PDK hardware and software, observe the following
recommendations:
•
J17 should be removed if the external clock source is used and the TOUT pin is still driven by a
processor in order to avoid conflicts.
•
Jumper J19 can be used to always select the 27MHz crystal (IOVDD position) or allow the
onboard/external clock selection to be controlled by GPIO5 (J5.19), as shown in
Figure 5 .
Figure 5. Jumper J19
The following section provides information on the analog input, digital control, and general operating
conditions of the ADS1278EVM.
Four of the analog input sources (channels 1–4) can be applied directly to J9 (top or bottom side) or
through signal-conditioning modules available for the the modular EVM system. Terminal block J7 is
connected in parallel with the analog signal connections to J9. The additional four channel sources (5-8)
can be applied to the terminal block J8.
Each input signal can be selected to connect directly to the analog inputs of the ADS1278 or they can use
the OPA1632 buffers that are provided. Switches S2–9 can be switched away from the ADS1278 to select
the Terminal Block (TBK) or towards the ADS1278 to select the Amplifier (AMP) for the analog inputs 1
through 8, as shown in
Figure 6 .
10 ADS1178EVM, ADS1278EVM, ADS1178EVM-PDK, and ADS1278EVM-PDK SBAU129C – November 2007 – Revised July 2008
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