MAX9268 Evaluation Kit

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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

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:

device sections are identical to the MAX9249 and

MAX9268 EV kits.

The audio section of the MAX9249 and MAX9259 EV

U25), which an be disabled by JU210 for applications

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

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.

EV kit and MAX9268 EV kit microcontrollers (U12) to be

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.

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-

SW122 resets the microcontroller, resending the audio