Cirrus Logic CDB5529 - Manual (Page 2)

CDB5529
2 DS246DB1
PART I: HARDWARE
Introduction
The CDB5529 evaluation board provides a quick
means of testing the CS5529 Analog-to-Digital
Converter (ADC). The board interfaces the
CS5529 to an IBM
TM
compatible PC via an
RS-232 interface while operating from either a sin-
gle +5 V supply or dual ±2.5 volt supplies. To ac-
complish this, the board comes equipped with an
80C51 microcontroller and a 9-pin RS-232 cable
which physically interfaces the evaluation board to
the PC. Additionally, analysis software provides
easy access to the internal registers of the convert-
er, and provides a means to display the converter’s
time domain, frequency domain, and noise histo-
gram performance. The evaluation board’s soft-
ware includes debug algorithms to trouble shoot
the evaluation board. Refer to the Trouble Shoot-
ing the Evaluation Board section for more details.
Evaluation Board Overview
The board is partitioned into two sections: analog
and digital. The analog section consists of the
CS5529 and a precision voltage reference. The dig-
ital section consists of the 80C51 microcontroller,
the hardware test switches, the reset circuitry, and
the RS-232 interface.
The CS5529 is designed to digitize signals while
operating from a 32.768 KHz crystal. As shown in
Figure 1, a signal can be connected to the convert-
er’s inputs via J1’s AIN+ and AIN- inputs. Note
that a simple RC network filters the input to reduce
broadband noise.
The evaluation board provides two voltage refer-
ence options, on-board and external. With HDR5’s
jumpers in positions 1 and 4, the LT1019 provides
an absolute voltage level of 2.5 volts (the LT1019
was chosen for its low drift, typically 5ppm/°C). By
setting HDR5’s jumpers to position 2 and 3, the
user can supply an external voltage reference to
J1’s REF+ and REF- inputs (Application Note 4 on
Crystal Semiconductor’s web site details various
voltage references).
The ADC serial interface is SPI
TM
and
MICROWIRE
TM
compatible. The interface control
lines (CS, SDI, SDO, and SCLK) are connected to
the 80C51 microcontroller via port one. To inter-
face an external microcontroller, these control lines
are also connected to HDR6. However to accom-
plish this, the evaluation board must be modified in
one of three ways: 1) cut the interface control traces
going to the microcontroller, 2) remove resistors
R1-R8, or 3) remove the microcontroller.
Figure 2 illustrates the schematic of the digital sec-
tion. It contains the microcontroller, a Motorola
MC145407 interface chip, and test switches. The
test switches aid in debugging communication
problems between the CDB5529 and the PC. The
microcontroller derives its clock from an 11.0592
MHz crystal. From this, the controller is configured
to communicate via RS-232 at 9600 baud, no pari-
ty, 8-bit data, and 1 stop bit.