Datasheet

MAX9268 Evaluation Kit
Evaluates: MAX9268
6 ______________________________________________________________________________________
The Interface History and Low Level Access tab
sheet (Figure 6) shows the recent low-level commu-
nications activity between the software GUI and the
MAX9249/MAX9268. The Register Access group box
provides arbitrary device read/write control, support-
ing additional user-supplied devices besides the on-
board MAX9249, MAX9268, and MAX7324. The Device
Address, Register, and Data drop-down lists specify
the device address and the register within the device, as
well as one optional byte of data to be written. Pressing
the Write Register button writes one byte of data to
the specified device register. Read Register reads the
specified device register and reports the results into the
Interface History window. Devices that are not register-
based (such as the MAX7324) are supported by Send
Data (no register) and Receive Data (no register).
User-supplied devices requiring other interface proto-
cols must use Raw TX byte codes to communicate.
Note that in bypass mode, raw data is passed to the
user-supplied slave device directly without modification.
Detailed Description of Hardware
The MAX9268 EV kit provides a proven layout for the
MAX9268. On-board level translators, I
2
S stereo audio
DAC, Class D audio power amplifier, and easy-to-use
USB-PC connection are included on the EV kit.
The MAX9268 EV kit board layout is divided into four
principal sections.
From header H1 to connector J1 are the support compo-
nents specific to the MAX9268. On-board LDO regulator
U2 powers the AVDD, DVDD, and IOVDD supplies from
VIN. Jumper JU9 optionally connects VIN to the link
cable, powering the remote EV kit board.
Below header H1, the board layout has three sections:
microcontroller (U10–U14), I
2
C slave device (U15), and
audio (U20–U25). The microcontroller and I
2
C slave
device sections are identical to the MAX9249 and
MAX9268 EV kits.
The audio section of the MAX9249 and MAX9259 EV
kits contain S/PDIF-to-I
2
S audio converter circuits (U20–
U25), which an be disabled by JU210 for applications
already having I
2
S audio.
The audio section of the MAX9268 EV kit contains an I
2
S-
to-audio DAC circuit (U20) and a Class D stereo power
amplifier (U25). The audio DAC circuits are similar to the
MAX9850 EV kit, and the power amplifier circuit is similar
to the MAX9701 EV kit.
User-Supplied Interface
To use the MAX9268 EV kit with a user-supplied inter-
face, first cut the PCB traces at jumpers JU141 and
JU142. Next, apply your own TX/SCL signal at the U1
side of JU141 and RX/SDA at the U1 side of JU142. Refer
to the MAX9249, MAX9259/MAX9260, and MAX9268 IC
data sheets for details about UART protocol for base
mode, write data format, read data format, selecting
base mode or bypass mode, and selecting UART or I
2
C
slave device.
User-Supplied Power Supply
The MAX9249 and MAX9268 EV kits are powered com-
pletely from the USB port by default. The 5V USB bus
power is supplied to the remote EV kit over the link cable
by default. Jumper JU10 powers the link cable (VBUS)
from the 5V USB supply, and jumper JU9 connects the
link cable VBUS to the VIN power supply.
To provide external power to each EV kit’s VIN, and still
power both microcontrollers from USB, remove the shunt
from JU9, but leave the shunt at JU10 installed. The link
cable carries the USB 5V bus power to the remote EV
kit board, but external user-supplied VIN supplies are
required to power the MAX9249 and the MAX9268.
To provide different power supplies to DVDD, AVDD, and
IOVDD, remove the shunts from jumpers JU21, JU22,
and JU23, and apply external user-supplied power at the
DVDD, AVDD, and IOVDD oval pads.
The I
2
S audio link demonstration requires both MAX9249
EV kit and MAX9268 EV kit microcontrollers (U12) to be
powered; otherwise, the on-board S/PDIF-to-I
2
S con-
verter or the I
2
S audio DAC does not initialize.
Detailed Description of Firmware
The DS89C450 microcontroller (U12) runs custom firm-
ware, which ensures that no breaks occur within reg-
ister read/write commands. The firmware records 9-bit
even-parity data received from the USB interface while
RTS is set, and plays back the 9-bit data with 1.5 stop
bits timing when RTS is cleared. Data received from the
MAX9268 is relayed to USB immediately.
The audio chips are initialized by an I
2
C command
sequence sent by the firmware when the microcon-
troller is reset. The same firmware runs on both the
MAX9249 and MAX9268 EV kit boards, so this initializa-
tion sequence covers both the S/PDIF-to-I
2
S converter
and the MAX9850 I
2
S stereo audio DAC. Pressing switch
SW122 resets the microcontroller, resending the audio
I
2
C initialization commands.