CMAXQUSB User’s Guide

4

Connectors P3 and P4 are designed to allow hardware

compatibility with previous Maxim EV kit module

designs. Headers P7 and P8 allow convenient probing

Connector P5 is used during factory test to program the

MAXQ2000 in-circuit using the JTAG interface. The

connector pinout is compatible with the MAXQ2000 EV

kit’s MAXQ-JTAG-001 board.

Platform Capabilities and Limitations

General-Purpose Input and Output (GPIO) Pins

LED1 is lit when VDD is powered. LED2, LED3, and LED4

are general-purpose software-controlled indicators, which

also connect to GPIO lines. When driven as inputs, the

output impedance should be less than 6000

Ω.

400kHz (full speed, the default) or 100kHz (slow speed).

Optional user-switchable SCL/SDA pullup resistors are

provided on-board. Your PC and its software limits

bursts at rated speed, but there is some variable “dead

time” between transfers due to communications over-

head. Properly written PC software can minimize this

dead time but cannot completely eliminate it.

SPI/3-Wire Interface

The CMAXQUSB module offers SPI at up to 8MHz,

using the default pin configuration. All four CPOL/CPHA

modes are supported. Your PC and its software limits

attainable throughput. The SPI bus runs in bursts at

rated speed, but there is some variable “dead time”

between transfers, due to communications overhead.

Properly written PC software can minimize this dead

time but cannot completely eliminate it.

Power Supply

The CMAXQUSB is powered by the host PC’s universal

serial bus (USB). The VDD system voltage can be con-

figured for direct USB 5V power, 3.3V, or 2.5V using

one of two on-board linear regulators. An optional

external 9V DC plug-in transformer (“wall wart”) can be

connected for any EV kit board that requires this unreg-

ulated 9V DC power supply. Both the unregulated

9V DC and regulated VDD power-supply voltages are

provided to the EV kit board on the 2 x 10 (P3) and

2 x 20 (P4) connectors. Current available to a compan-

ion EV kit is 80mA.

During USB suspend, the FT232BM drives the MAX890

into a partially powered mode, bringing VDD up to

approximately 1.8V. No commands are sent to the

firmware during this mode, so there is no impact.

However, custom designs not requiring USB suspend

should consider removing the MAX890 to avoid this

problem.

Scripting and Data Acquisition

The CMAXQUSB can store a script of commands in its

internal memory to eliminate communication “dead

time.” A script may be repeated up to 256 times, but

branching and decision making are not supported. A

script may also have a maximum of 126 command/data

bytes. Up to 1024 bytes of data may be collected.

SDA. The CMAXQUSB provides 1.5k

Ω pullup resistors,

enabled by setting both circuits of DIP switch SW1

“ON.” If there are pullup resistors already on the bus,

disable the CMAXQUSB’s pullup resistors by setting

both circuits of SW1 “OFF.”

JUMPER

POSITION

FUNCTION

2.5V

3.3V

JU1 VDD

SELECT

5V

J2

(underneath

SW1)

Open

Factory assembly option:

replaces SW1-1.

J3

(underneath

SW1)

Open

Factory assembly option:

replaces SW1-2.

JU2

Closed

Connects MAXQ2000 P6.2 to

P6.3, supporting the Maxim

1-Wire® interface.

Open

JTAG connector P5 does not

connect to the +5V supply.

JU4

Closed

JTAG connector P5 connects to

the +5V supply.

Open

Optional higher voltage

unregulated power supply is left

unconnected; connector P1 is

not used.

JU5

Closed

Enable optional unregulated

power supply from P1 to

connectors P3 and P4.

Jumper Tables

1-Wire is a registered trademark of Maxim Integrated Products, Inc.