DS3900K# Maxim Integrated Products, DS3900K# Datasheet - Page 3

• Manufacturer Part Number: DS3900K#
• Description: Power Management Modules & Development Tools 2-WIRE BUS INTERFACE NTERFACE EV KIT ROHS
• Manufacturer: Maxim Integrated Products

Specifications of DS3900K#

• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

The DS3900 communicates with ICs using a PC’s serial
port. It utilizes a MAX3223 RS232 transceiver to trans-
late the serial port signal levels from
able levels for a microprocessor. The microprocessor is
then able to communicate to the PC by using its univer-
sal asynchronous receiver transmitter.
In addition to the serial communication channel that is
routed through the MAX3223, the data terminal ready
(DTR) signal is routed through the secondary channel
to produce a control signal that can reset the DS3900
from software. The software-reset function primarily
allows the PC to search its available serial ports to find
the DS3900.
After a reset occurs, the DS3900 writes a banner over
the serial port that allows the PC to detect its presence.
Once it has been detected, the PC sends simple 2-byte
commands over the serial connection, which provides
instruction and data for the DS3900 to communicate
with 2-wire parts, or to read or write a specific pin of the
DS3900. All of the pins, with the exception of P3, have
tristate drivers. P3 has an open-drain output, and can
be read as an input pin as well; however, its default
function is a system pulse that provides a visual indica-
tion (through an LED) that the DS3900 is operating
properly. The P3 pin defaults to a slow-pulsing output,
but this can be disabled, enabling P3 as an I/O pin, or it
can be adjusted to a faster pulse rate as an indicator
for the application.
Because it is rated to work with supply voltages ranging
from +3.0V to +5.5V, the DS3900 operates from the
Figure 1. Functional Diagram
PC
N.C.
Detailed Description
DS3900 SERIAL COMMUNICATION MODULE
DTR
T
R
N.C.
X
X
_____________________________________________________________________
±12V to accept-
R2IN
R1IN
T1OUT
T1OUT
Serial Communications Module
TRANSCEIVER
MAX3223
R2OUT
R1OUT
T1IN
T2IN
same voltage supply as the IC that it is controlling in
most cases.
The DTR signal of the serial port (pin 4 of a DB9 con-
nector) is routed through the second channel of the
MAX3223 transceiver. DTR controls an NMOS, which is
connected to the reset signal of the microprocessor.
This allows the PC to hold the DS3900 in reset until it is
ready for operation, or to reset the DS3900 in the event
an error occurs. Although the reset signal is accessible
through the DS3900’s connector, it should be left dis-
connected so it can be controlled through software.
When DTR transitions to ON, the DS3900 exits its reset
state and executes its initialization code. The initializa-
tion routine writes a banner (see DS3900 Revisions sec-
tion), “DSIO r2.0” over the serial connection to the PC,
which can be used by the PC to identify that the
DS3900 is present. After it has left the reset state, all of
the DS3900 signals, except P3, are configured as
inputs (the output drivers are disabled). P3 appears as
an output and begins to pulse slowly. If the switches
enable SDA’s and SCL’s pullups, those signals float
high, and all the other pins float to an undetermined
state if they are not being driven by external signals.
The DS3900 has custom firmware that enables fast
communication to 2-wire devices. To utilize this
firmware, connect the SCL bus to P10 and the SDA bus
to P11. Additionally, it has built-in pullup resistors that
can be utilized by turning both switches on (see Using
V
Designing Hardware to Utilize the Built-in
CC
2.2kΩ
For Evaluation Kits
RESET
SERIAL
COMM
MICROPROCESSOR
PULSE (P3)
SDA (P11)
SCL (P10)
SWITCH
P1, P2,
P4–P9
Support for 2-Wire Devices
4.7kΩ
Resetting the DS3900
8
4.7kΩ
V
CC
330Ω
8 GENERAL-PURPOSE
DIGITAL I/O SIGNALS
2-WIRE INTERFACE
LED PULSE
3