Texas Instruments ADS7881, User Manual, Page: 4 / 23

1.2.2 Reference
The ADS78x1EVM provides an onboard 2.5-V reference circuit. The EVM also supplies a reference voltage via
connecter P1 pin 20. This reference voltage can be filtered through amplifier U1. The converter itself has on-chip
reference buffer, and therefore does not need to be buffered externally. The reference buffer circuit on the EVM
is used to generate the offset voltage for the input amplifier, U2.
The EVM allows selection from three reference sources. Set SJP1, SJP2, and SJP4 to select either an onboard
reference voltage (REF1004-2.5), ADC internal reference, or a user-supplied reference voltage via P1 pin 20.
Table 1-3 lists jumper settings and Section 5 provides full schematics.
Table 1-3. Solder Short Jumper Setting
Reference
Designator
Description
Pads
1–2 2–3
SJP1 Apply onboard reference directly to SJP2 pin 3 Installed
(1)
—
Apply buffered reference voltage to SJP2 pin 3 — Installed
SJP2 Apply internal reference to REFIN pin Installed
(1)
—
Apply external reference to REFIN pin — Installed
SJP4 Apply onboard reference to U1, reference buffer Installed —
Apply user-supplied reference to U1, reference buffer — Installed
SJP5 Apply DC offset to input signal Installed
(1)
—
SJP6 Short to pin 4 of amplifier U1 to ground Installed —
Short to pin 4 of amplifier U1 to –VCC — Installed
(1)
SJP7 Short to pin 4 of amplifier U2 to ground Installed —
Short to pin 4 of amplifier U2 to –VCC — Installed
(1)
(1) Factory-set condition.
1.3 Digital Interface
The ADS78x1EVM is designed for easy interfacing to multiple platforms. Samtec part numbers SSW-110-22-F-
D-VS-K, TSM-110-01-T-DV-P, SSW-116-22-S-D-VS, and TSM-116-01-T-D-V-P provide a convenient dual row
header and socket combination at P1, P2, P3, and J3. Consult Samtec at www.samtec.com or 1-800-SAMTEC-9
for a variety of mating connector options.
Connectors P1, P2, and P3 allows the user to plug the EVM into the 5-6k interface card to interface directly with
the TMS320C5000 and TMS320C6000 series of DSP.
Table 1-4 lists the connector pin out.
Table 1-4. Pin Out for Parallel Control Connector P2
Connector.Pin
(1)
Signal Description
P2.1 DC_CS Daughter card board select pin
P2.3 — —
P2.5 — —
P2.7 A0 Address line from processor
P2.9 A1 Address line from processor
P2.11 A2 Address line from processor
P2.13 — —
P2.15 — —
P2.17 — —
P2.19 BUSY Busy signal from converter. W4 must be shorted.
(1) All even-numbered pins of P2 are tied to DGND.
Read (RD), conversion start (CONVST) and reset (RESET) signals to the converter can be assigned to two
different addresses in memory via jumper settings. The jumper settings allow up to two ADS78x1EVMs to be
stacked into processor memory. See
Table 1-5 for jumper settings. The evaluation module does not allow the
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4 ADS7881EVM, ADS7891EVM Evaluation Module SLAU150A – DECEMBER 2004 – REVISED OCTOBER 2021
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