DS3900K# Maxim Integrated Products, DS3900K# Datasheet - Page 4

• 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

Serial Communications Module
For Evaluation Kits
Integral Pullups section). This connects 4.7kΩ resistors
to both 2-wire buses.
For designs that only use the DS3900 to communicate
to 2-wire devices, the following items must be account-
ed for in the hardware design:
1)
2)
3)
4)
5)
6)
Utilizing the DS3900 for general-purpose bit I/O is
equally simple as using it for 2-wire applications. All of
the I/O pins with the exception of P3 have tristate out-
puts. These signals can be written to a ‘0’ or a ‘1’, and
they can be read as inputs. P3 has an open-drain out-
put, and can also be read as input. Because it defaults
to a pulsing output, P3 is generally connected to an
LED as shown in the Typical Operating Circuit. Writing
it to a ‘1’ turns off the pulldown transistor, which turns
the LED off, and writing it to a ‘0’ turns the pulldown
and the LED on. This can also be used as an open-col-
lector I/O pin with an external pullup resistor and no
LED, making the pin appear as a normal output. The
pulse function can be disabled in software, but designs
using P3 for I/O should be conscious that the DS3900
could attempt to blink P3 before the pulse function is
disabled. As long as the IC connected to P3 is tolerant
of this behavior, P3 can be used as an additional I/O.
Additionally, designs using P10 and P11 should be
conscious of the built-in pullup resistors that are intend-
ed for use with 2-wire devices (see Using Integral
Pullups section for details).
The general procedure for connecting the DS3900 for
bit I/O applications is as follows:
1)
2)
4
Designing Hardware to Utilize the General-
_____________________________________________________________________
Place the mating connectors on the circuit board
(see Figure 5).
Connect V
Connect the SCL bus to pin P10, and the SDA bus
to P11 of the DS3900.
If the application board does not have pullup
resistors, turn the switches on to enable the on-
board pullups; otherwise, turn the switches off to
disconnect the integrated pullups.
Optional: connect an LED to P3 for the pulse func-
tion (see Typical Operating Circuit).
Drive the DS3900 with either evaluation software pro-
vided by Dallas Semiconductor or custom-designed
software for the end application (see Writing Software
to Interface with the DS3900 section).
Place the mating connectors on the circuit board
(see Recommended PC Board Connection).
Connect V
CC
CC
and all three ground terminals.
and all three GND ground terminals.
Purpose Bit I/O Signals
3)
4)
5)
The DS3900 interprets 2-byte instructions (see Table 1)
sent from a PC to determine what to do. After a valid
command is received, it will begin to execute the com-
mand. Upon completion, it will return any data associat-
ed with the command, plus a unique acknowledgement
byte that informs the PC that the command completed
successfully. If an invalid command was received or
the command did not complete successfully, the
DS3900 will return error code (0xFA).
Because the DS3900 could return 0xFA as data, it is
important that the PC software is aware of the amount
of data that it should expect to be returned. For exam-
ple, if a 2-wire read operation is performed and a signal
byte, 0xFA, is returned, then the PC is receiving an
error code because the 2-wire read command should
return first the data, then the acknowledgement. If the
data was 0xFA, the DS3900 would return 0xFA followed
by the command acknowledgment 0xB2.
Revisions yielding significant changes and/or improve-
ments can be tracked by reading the banner after a
reset or by calling the Read Revisions command
(0xC2). The Read Revisions command (added in Rev.
2.0) will return three bytes: the major revision, the minor
revision, and a command acknowledgement (0xD2).
For example, if the DS3900's revision is 2.0, it will return
a major revision of 2, a minor revision of 0, and the
command acknowledgement 0xD2.
Knowing the revision allows the software to both utilize
new functions that are not available in previous ver-
sions of the DS3900's firmware and to avoid using com-
mands that are not present in prior versions. Although
there are no plans to change the firmware at this time,
Dallas Semiconductor reserves the right to change the
firmware at any time without notice.
Connect P1 through P11 to the application. If the
application is using 2-wire devices in addition to
the remaining bit I/O signals, make sure to reserve
P10 and P11 for the 2-wire application. Use P3
only if the application is able to tolerate the pulse
function until it is disabled.
Optional: connect an LED to P3 for the pulse func-
tion (see Typical Operating Circuit).
Write software to allow the DS3900 to communi-
cate with the target IC.
Writing Software to Interface
with the DS3900
DS3900 Revisions