General-Purpose Two-Wire Interface Utility

The General-Purpose Two-Wire Interface Utility is used

to communicate with the MAX7313 and thus controls or

reads back signals from the MAX5946L. The utility con-

figures the SMBus interface parameters such as Start

and Stop bits, Acknowledgements, and clock timing.

The Two-Wire Interface screen allows you to send

general-purpose SMBus commands using the

SMBusWriteByte and SMBusReadByte. All data is in

hexadecimal format.

The “Hunt for active listeners” button scans the entire

2-wire address space, reporting each address that is

acknowledged. The SMBusWriteByte transmits the

device address, command, and one byte of data. The

SMBusReadByte transmits the device address, a com-

mand, and then retransmits the device address and

reads one byte of data.

Software Quick Start

1) Install shunts on pins 2 and 3 of jumpers JU5–JU8

(computer control) on the MAX5946L EV kit.

2) Connect the CMODUSB interface board to the

MAX5946L EV kit’s J4 connector.

3) Set both CMODUSB SW1 switches to enable.

These provide pullup resistors for the SMBus.

4) Connect the computer’s USB port to the CMODUSB

interface board with a USB cable.

5) Install the MAX5946L evaluation software on your

computer by running the INSTALL.EXE program on

the CD-ROM disk. The program files are copied

and icons are created for them in the Windows Start

menu. Restart the computer when prompted. For

Windows 2000 or XP, you may need administrator

privileges.

6) Turn on the power supplies for the EV kit.

7) Start the MAX5946L program by opening its icon in

the Start menu.

8) Configure the MAX7313 I/O Expander for operation

as follows.

Port configuration:

•

Configure the MAX7313 ports to Inputs/Outputs

per Tables 5 and 6 above by using the

SMBusWriteByte command to write 0x33 data

to command bytes 0x06 and 0x07.

Reading from channels A or B:

•

To

read

a

specific

channel,

use

the

SMBusReadByte command. Use the 0x00

command byte for reading the ports on channel

A. Use the SMBusReadByte command and the

0x01 command byte for reading the ports on

channel B.

Writing to channels A or B:

•

To write a specific channel, use the

SMBusWriteByte command. Use the 0x02

command byte for writing to the ports on chan-

nel A. Use the SMBusWriteByte command and

the 0x03 command byte for writing to the ports

on channel B. Enter the desired hexadecimal

data in the Dataout Edit field.

•

When writing to an output (0x03, 0x04) the data

corresponding to input bits are ignored and are

therefore “don’t care” bits.

The main window hexadecimal and binary combo boxes

can be used to convert between both number formats.

The general-purpose Two-Wire Interface Utility only

accepts and outputs a hexadecimal number format.

General Troubleshooting

Problem: Software reports it cannot find the board.

•

Is the CMODUSB board power LED lit?

•

Is the USB communications cable connected?

•

Has Windows plug-and-play detected the board?

Bring up Control Panel->System->Device Manager,

and look at what device nodes are indicated for

USB. If there is an “unknown device” node attached

to the USB, delete it—this forces plug-and-play to

try again.

Problem: Unable to find DUT (device under test).

•

Are the SCL and SDA signals pulled up to VDD? The

CMODUSB dip-switch SW1 enables the on-board

resistors on the CMODUSB interface board. There

must be pullup resistors somewhere on the bus.

•

If using jumper wires to connect, could the SCL and

SDA signals be swapped? Could the ground return

be missing?

MAX5946L Evaluation Kit/Evaluation System

8

_______________________________________________________________________________________