Rev 1; 7/04
Serial Communications Module
For Evaluation Kits
The DS3900 provides bidirectional communication with
2-wire and 3-wire devices using a PC’s serial
port. In addition, it can also be used as a general-purpose digital I/O interface with 11 I/O signals that can
evaluate a wide variety of ICs.
The DS3900 is intended for evaluation purposes only.
Features
♦ Communicates from PCs to ICs Through a
Serial Port
♦ Fast Communication to 2-Wire Devices
♦ Eleven General-Purpose Digital I/O Pins,
Including SDA and SCL
♦ Built-in Pullup Resistors for SDA and SCL
Minimize Required External Hardware
Applications
Prototyping 2-Wire and 3-Wire Device Designs
Evaluating 2-Wire and 3-Wire Devices
♦ Connection to Standard Prototyping Boards
Possible Using Header Connectors
♦ Operates from 3.0V to 5.5V
Building Test Software for Systems Containing
2-Wire or 3-Wire Devices
Communicating With ICs that Require up to 11 I/O
Signals
Ordering Information
PART
DESCRIPTION
DS3900EVKIT
DS3900 Module
DS3900 Photo
Pin Configuration
P1
P2
DS3900 R1.0
P11 / SDA
P10 / SCL
C4
U1
P3
GND
(N.C.) RESET
X1
VCC
C6
GND
P9
P4
P8
P5
C1
P7
C5
GND
P6
JP1
SCL
R2
SDA
R3
JP2
Typical Operating Circuit appears at end of data sheet.
______________________________________________ Maxim Integrated Products
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.
1
DS3900
General Description
DS3900
Serial Communications Module
For Evaluation Kits
RECOMMENDED OPERATING CHARACTERISTICS
(VCC = 3.0V to 5.5V, TA = +25°C.)
PARAMETER
SYMBOL
CONDITION
MIN
Supply Voltage
VCC
(Note 1)
+3.0
Input Logic 0
VIL
(Note 2)
0
Input Logic 1
VIH
(Note 2)
0.8 x
VCC
Supply Current
ICC
VCC = 5V
TYP
RS232 Baud Rate
MAX
UNITS
+5.5
V
0.15 x
VCC
V
VCC
V
5.0
mA
57600
bps
Note 1: All voltages listed are with respect to ground.
Note 2: Devices are only functionally tested; all of the DC parametric values listed are designed parameters.
Pin Description
PIN
P1, P2, P4 TO P9
P3/PULSE
Pulse or general-purpose bit I/O with open-drain I/O pin (input, open-drain output driver)
P10
SCL (open-drain output when used as SCL) or general-purpose bit I/O with tristate I/O pin (input,
totem-pole output driver)
P11
SDA (open-drain output or input when used as SDA) or general-purpose bit I/O with tristate I/O pin
(input, totem-pole output driver)
RESET (N.C.)
2
FUNCTION
General-purpose bit I/O with tristate I/O pin (input, totem-pole output driver)
Do not connect (reset for microprocessor). This pin is controlled by application software through the
serial port’s DTR signal.
GND
Ground Terminals. All three ground terminals must be connected to ground for operation.
VCC
Power Supply Terminal
_____________________________________________________________________
Serial Communications Module
For Evaluation Kits
DS3900
VCC
DS3900 SERIAL COMMUNICATION MODULE
VCC
2.2kΩ
N.C.
4.7kΩ
4.7kΩ
330Ω
SWITCH
MICROPROCESSOR
DB9
MAX3223
TRANSCEIVER
PC
DTR
TX
RX
N.C.
LED PULSE
PULSE (P3)
R2IN
R2OUT
RESET
SDA (P11)
R1IN
R1OUT
SERIAL
COMM
SCL (P10)
T1OUT
T1IN
T1OUT
T2IN
P1, P2,
P4–P9
2-WIRE INTERFACE
8
8 GENERAL-PURPOSE
DIGITAL I/O SIGNALS
Figure 1. Functional Diagram
Detailed Description
The DS3900 communicates with ICs using a PC’s serial
port. It utilizes a MAX3223 RS232 transceiver to translate the serial port signal levels from ±12V to acceptable levels for a microprocessor. The microprocessor is
then able to communicate to the PC by using its universal 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 indication (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
same voltage supply as the IC that it is controlling in
most cases.
Resetting the DS3900
The DTR signal of the serial port (pin 4 of a DB9 connector) 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 disconnected so it can be controlled through software.
When DTR transitions to ON, the DS3900 exits its reset
state and executes its initialization code. The initialization routine writes a banner (see DS3900 Revisions section), “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.
Designing Hardware to Utilize the Built-in
Support for 2-Wire Devices
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
_____________________________________________________________________
3
DS3900
Serial Communications Module
For Evaluation Kits
Integral Pullups section). This connects 4.7kΩ resistors
to both 2-wire buses.
3)
For designs that only use the DS3900 to communicate
to 2-wire devices, the following items must be accounted for in the hardware design:
1)
2)
3)
4)
5)
6)
Place the mating connectors on the circuit board
(see Figure 5).
Connect VCC and all three ground terminals.
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 onboard pullups; otherwise, turn the switches off to
disconnect the integrated pullups.
Optional: connect an LED to P3 for the pulse function (see Typical Operating Circuit).
Drive the DS3900 with either evaluation software provided by Dallas Semiconductor or custom-designed
software for the end application (see Writing Software
to Interface with the DS3900 section).
Designing Hardware to Utilize the GeneralPurpose Bit I/O Signals
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 outputs. These signals can be written to a ‘0’ or a ‘1’, and
they can be read as inputs. P3 has an open-drain output, 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-collector 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 intended 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) Place the mating connectors on the circuit board
(see Recommended PC Board Connection).
4)
5)
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 function (see Typical Operating Circuit).
Write software to allow the DS3900 to communicate with the target IC.
Writing Software to Interface
with the DS3900
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 command. Upon completion, it will return any data associated 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 example, 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.
DS3900 Revisions
Revisions yielding significant changes and/or improvements 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 versions of the DS3900's firmware and to avoid using commands 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.
2)
Connect VCC and all three GND ground terminals.
4
_____________________________________________________________________
Serial Communications Module
For Evaluation Kits
DS3900
Table 1. DS3900 Command Protocol
COMMAND
1ST BYTE SENT
2ND BYTE SENT
RETURNED BYTE(S)
0x8%
% = number of bytes to
write -1
Memory address
followed by %+1 data
bytes
0x8% Command Successful
0xFA Command Failed
0x9%
% = number of bytes to
read -1
Memory Address
(%+1) Data bytes followed by
0x9% Command Successful
0xFA Command Failed
2-Wire Start*
(and Repeated Start)
0xA0
0x00, Ignored
0xB0 Command Successful
0xFA Command Failed
2-Wire Write Byte*
0xA1
Data
0x00-0xFF Valid
0xB1 Command Successful
0xFA Command Failed
Packet Write*
Packet Read*
2-Wire Read Byte*
0xA2
Acknowledge
0x01 ACK
0x00 NACK
1st Returned Byte
Data
2nd Returned Byte
0xB2 Command Successful
0xFA Command Failed
2-Wire Stop*
0xA3
0x00, Ignored
0xB3 Command Successful
0xFA Command Failed
Toggle SCL 9 Times
0xA4
0x00, Ignored
0xB4 Command Successful
0xFA Command Failed
Set Packet Device Address*
0xA5
Device Address
0x00-0xFE
Even Values Only
0xB5 Command Successful
0xFA Command Failed
Pulse Enable/Disable
(Available after Rev 1.1)
0xC0
0x00 Disable
0x01 Enable
0xD0 Command Successful
0xFA Command Failed
Pulse Fast/Slow
(Available after Rev 1.1)
0xC1
0x00 Pulse Slow
0x01 Pulse Fast
0xD1 Command Successful
0xFA Command Failed
Read Revision
(Available after Rev 2.0)
0xC2
0x00, Ignored
1st Returned Byte
Major Revision
2nd Returned Byte
Minor Revision
3rd Returned Byte
0xD2 Command Successful
0xFA Command Failed
Bit I/O Read**
0xE#
# determines pin to read.
(See Table 2)
0x00, Ignored
0x00 Pin P# Low
0x01 Pin P# High
0xFA Command Failed
Bit I/O Write**
0xF#,
# determines pin to write.
(See Table 2)
Write Pin P#
0x00 Low
0x01 High
0xF0 Command Successful
0xFA Command Failed
*See Using the DS3900 with 2-Wire Devices section.
**See Using the DS3900's General-Purpose Bit I/O Signals section.
_____________________________________________________________________
5
DS3900
Serial Communications Module
For Evaluation Kits
Table 2. Bit I/O Addresses
Table 3. DS3900 Revisions
BIT I/O PIN ADDRESS #
DS3900 PIN
1
P1
2
P2
3
P3
4
P4
5
P5
6
P6
7
P7
8
P8
9
P9
A
P10
B
P11
Using the DS3900 with 2-Wire Devices
There are two modes that can be used to communicate
with 2-wire devices. There is an individual command
mode that allows the PC to control exactly what is written over the 2-wire bus, and a packet-based mode that
automatically sends the start, device address, data
address, and the stop commands.
When using the individual command mode, the PC
sends out individual commands to issue 2-wire start
conditions, stop conditions, write data, and read data
with or without acknowledgement. After each command
is sent, the DS3900 executes the command and returns
the individual 2-wire command's acknowledgement
code. If an error occurs, the DS3900 will return 0xFA.
For a complete listing of commands see Table 1.
To help with using the individual commands, two examples showing writing to and reading from a DS1803 are
shown in Tables 4 and 5. The assumption made for
addressing the DS1803 is that all three addressing pins
(A0, A1, and A2) are grounded. Packet mode was
added in revision 2.0 of the firmware, and it is supported by 3 new commands: Set Packet Device Address
(0xA5); Packet Write (0x8%); and Packet Read (0x9%).
The Set Packet Device Address command is used to
set the 2-wire device address used by the Packet Read
and Packet Write commands. The Set Packet Device
Address command should be called before any packet
reads or writes to ensure that communications are initiated at the intended device address. Once the packet
device address is set, it will remain set until it is
changed again by calling the Set Packet Device
Address function, or the power is cycled. Upon initial
power-up, this value is indeterminate, so it should be
reset to the desired value when there is any doubt
6
REVISION
DS3900 BANNER
DESCRIPTION
DSIO r1.0
Original Issue. P3 is not
utilized for the pulse
function, it is opencollector I/O only.
1.1
DSIO r1.1
The pulse functions were
added, changing P3’s
primary function.
Commands 0xC0 and
0xC1 were added.
2.0
DSIO r2.0
Major rev = 2
Minor rev = 0
Packet read and write,
packet address, and
read revision commands
added.
1.0
about its current state. If the value is successfully
changed, the DS3900 will return an acknowledgement
of 0xB5, and if an error occurs, 0xFA will be returned.
Note: The value sent to the DS3900 with the Set Packet
Device Address command should always be an even
value (e.g. 0xA0, 0xA2). The DS3900 automatically
controls the read/write bit of the device address during
packet read and write operations. Failure to send even
values will result in communication problems.
The Packet Write command allows up to 16 data bytes
to be sent from the PC to a 2-wire device with a single
command. The data will be written to the device
address set using the Set Packet Device Address command. To initiate a Packet Write command, the first
byte sent to the DS3900 is 0x8%, where % is one less
than the number of bytes to be written (e.g. 0x80 hex
writes one byte). The second byte sent to the DS3900
is the starting memory address to write the data, which
is followed immediately by %+1 data bytes. Once the
DS3900 has received the entire packet of data, it will
begin sending it to the 2-wire device. The Packet Write
command monitors the 2-wire communication to ensure
that the 2-wire device is acknowledging every byte of
the data transmission. If every byte of the Packet Write
is acknowledged, the DS3900 sends 0x8% back to the
PC. If all bytes are not acknowledged, the DS3900
returns 0xFA.
Because the Packet Write forces the following order of
events during the 2-wire communication to be: start
condition, write the device address, write the memory
address, write the data[1...16], stop condition, it may
not work with all devices. Use the individual 2-wire
commands if the packet write is not compatible with a
particular 2-wire device.
_____________________________________________________________________
Serial Communications Module
For Evaluation Kits
DS3900
Table 4. Example of Writing to a DS1803
SEQ #
SEND START COMMAND, WRITE 0x23 TO POT 0, AND 0X34 TO POT 1, SEND STOP COMMAND
1ST BYTE SENT
2ND BYTE SENT
1ST BYTE RETURNED 2ND BYTE RETURNED
1
0xA0
0x00
Place holder
0xB0
Command ack
None
2-wire start
2
0xA1
0x50
Data
0xB1
Command ack
None
Send 0x50 over
2-wire bus
(send write DS1803 addr)
3
0xA1
0xA9
Data
0xB1
Command ack
None
Send 0xA9 over
2-wire bus
(write pot 0 command)
4
0xA1
0x23
Data
0xB1
Command ack
None
Send 0x23 over
2-wire bus
(write 0x23 to pot 0)
5
0xA1
0x34
Data
0xB1
Command ack
None
Send 0x34 over
2-wire bus
(write 0x23 to pot 1)
6
0xA3
0x00
Place holder
0xB3
Command ack
None
2-wire stop
Example: Sending the byte sequence {0x82, 0x20,
0x45, 0x67, 0x89} to DS3900 causes it to:
1. Send a 2-wire Start condition.
2. Write the device address R/W =0 (previously set
using Set Packet Device Address).
3. Write the memory address (0x20).
4.
5.
6.
7.
Write data 0x45 (to address 0x20).
Write data 0x67 (to address 0x21).
Write data 0x89 (to address 0x22).
Send a 2-wire Stop condition.
8.
If the 2-wire device acknowledges all bytes of the
data transmission, the DS3900 will return (0x82);
otherwise it will return an error code (0xFA).
The Packet Read command allows up to 16 data bytes
to be read with a single 2-byte instruction. The read
operation will be sent to the device operating at the
device address set using the Set Packet Device
Address command. The first byte sent for a Packet
Read command is 0x9%, where % is one less than the
number of bytes to read (e.g. 0x95 reads 6 bytes). The
second byte sent determines the memory address to
begin reading from within the device that is being
addressed. After the second byte is received, the
DS3900 will begin a dummy write cycle that will
address the part as if writing, and write out the device
DESCRIPTION
address followed by the memory address. Then a
restart condition is generated, and the device's read
address is sent to start the read operation. The DS3900
will begin reading the data from the 2-wire part and
sending it back to the PC. The DS3900 will acknowledge all but the last data byte sent from the 2-wire part.
The last byte is Not Acknowledged, which is a standard
2-wire practice. Once it has read %+1 data bytes and
sent them to the PC, the DS3900 will send 0x9% if the
read occurred without error, or 0xFA if a problem did
occur.
Example: Sending the byte sequence {0x91, 0x20} to
the DS3900 will cause it to:
1. Send a 2-wire Start command.
2. Write the device address R/W =0 (set previously
using Set Packet Device Address).
3. Write the memory address 0x20.
4. Send a 2-wire Start command (repeated-start).
5. Write the device address R/W =1 (set previously
using Set Packet Device Address).
6. Read the data (at address 0x20), send 2-wire
Acknowledge on 9th clock cycle, and send the
data read back to the PC.
7. Read the data (at address 0x21), send 2-wire Not
Acknowledge on 9th clock cycle, and send the
data read back to the PC.
_____________________________________________________________________
7
DS3900
Serial Communications Module
For Evaluation Kits
Table 5. Example of Reading from a DS1803
SEQ #
SEND START COMMAND, READ 0x23 FROM POT 0 AND 0x34 FROM POT 1, SEND STOP COMMAND
1ST BYTE SENT
2ND BYTE SENT
1ST BYTE RETURNED
2ND BYTE
1
0xA0
0x00
Place holder
0xB0
Command ack
None
2-wire start
2
0xA1
0x51
Data
0xB1
Command ack
None
Send 0x51 over
2-wire bus
(send read DS1803 addr)
3
0xA2
0x01
Read with ack
0x23
Data
Read with nack
1st return byte 0x34
(data from pot 1)
2nd return byte 0xB2
(command ack)
0xA2
0x00
Read with nack
0x34
Data
0xB2
Command ack
5
0xA3
0x00
Place holder
0xB3
Command ack
None
Send a 2-wire Stop command.
If the transmission occurred without errors detected, return the command acknowledgement (0x91),
else return the error code (0xFA).
Because the Packet Read command assumes that the
memory address should be sent out with a dummy
write cycle before a restart with the read device
address, it may not work with some devices. In cases
where it is not appropriated, use the individual 2-wire
commands.
Resetting the 2-Wire Bus
The only 2-wire command that is in Table 1 and not listed in either example of the 2-wire section is toggle SCL
nine times. This is used to reset the 2-wire bus in the
event that there is a communications breakdown while
the slave is holding SDA low.
When a slave holds SDA low, a stop command cannot
be issued since it requires SDA to transition from lowto-high while the clock is high. For the transition from
low-to-high to happen, both the slave and the master
have to release their SDA pulldown transistors. To reset
the bus, send out the command to toggle SCL nine
times followed by a stop command. This clocks the 2wire bus nine times, so if a read operation was disturbed, the slave is clocked until it is expecting
acknowledgement from the master. At the time it is
8
0xB2
Command ack
Read with nack
1st return byte 0x23
(data from pot 0)
2nd return byte 0xB2
(command ack)
4
8.
9.
DESCRIPTION
2-wire stop
expecting acknowledgement, it releases the bus, and
is clocked at least once more, providing a NAck condition. Once the nine clock cycles are sent, the slave
should no longer be controlling SDA signal. This allows
the DS3900 to issue a stop command. When the stop
command occurs, all slaves on the 2-wire bus should
respond to their addresses.
The Pulse Commands
The pulse commands enable or disable the pulse function, and set the pulse rate to either fast (7.37Hz) or slow
(0.92Hz). If P3 was last used as an input, P3 must be
written to either a 1 or a 0 to make it appear as an output for the pin to toggle. If left as an input, the register
controlling P3 will toggle, but the pin will not because
the driver is not enabled. On power-up P3 is set to an
output, and the pulse will begin at the slow rate.
Using the DS3900’s General-Purpose Bit I/O Signals
Reading and writing individual DS3900 pins is done by
using the bit I/O commands 0xE# and 0xF# respectively, where # (Table 2) represents an individual pin on the
DS3900. For example, the command 0xE2, places the
P2 output driver in a high-impedance state and reads
the pin as an input.
Writing to a pin sets it to the desired state and leaves it
there until it is written to the opposite state or a read
command issued. When a read is performed, the driver
_____________________________________________________________________
Serial Communications Module
For Evaluation Kits
Application Information
Decoupling the DS3900’s VCC Supply
The DS3900 has decoupling on its PC board, but due to
the high periodic current draw of the RS232 transceiver.
It is recommended to place a decoupling capacitor
(47µF, Tantalum capacitor) next to the connector on the
board that the DS3900 will be mounted.
Using the Integral Pullups
Moving the switches to the on (labeled “ON” on the
switch) position enables the integral pullups. This connects 4.7kΩ pullup resistors to the SDA and SCL
buses, and it eliminates the need to place external
pullup resistors on the application board for 2-wire
communication. In the event that the application board
already has pullups present, disconnect the integral
pullups by placing the switches in the off position. This
eliminates the extra (unnecessary) pullup strength,
because having both the integral pullup and the application board’s pullup on at the same time could potentially cause problems for either the DS3900 or the
2-wire slaves, which are required to pull the buses low.
Additionally, when P10 and P11 are used as bit I/O
pins, it can be advantageous to disconnect the pullups
to reduce the through current when either signal is driven low. For bit I/O operations, writing the signal to a ‘1’
enables a PMOS driver that drives the signal high.
However, it is also possible to use P10 and P11 as
open-collector I/O pins by enabling the pullups and
performing only read and write ‘0’ operations. As long
as a ‘1’ is never written to P10 or P11 it appears as an
open-collector output. This is how the firmware manufactures the open-collector output for the 2-wire interface.
Intended Use
The DS3900 module and the bundled software are
intended only to be used to evaluate Maxim and Dallas
Semiconductor’s integrated circuits. The software is provided “as is”, without warranty of any kind, express or
implied, including but not limited to the warranties of
merchantability, fitness for a particular purpose and noninfringement. In no event shall Dallas Semiconductor be
liable for any claim, damages or other liability, whether in
an action of contract, tort or otherwise, arising from, out
of, or in connection with the software or the use or other
dealings in the software.
_____________________________________________________________________
9
DS3900
is tristated and the input is read. The pin remains in a
high-impedance state until a write operation is performed. As mentioned before, all I/O pins, except P3,
are inputs on power-up.
Note: If an I/O pin is being used for both reads and
writes, take care to avoid bus contention.
Since software can only change a single pin at a time,
the DS3900 is much slower when communicating using
the bit I/O commands. For some applications, this is
acceptable since the 57600 baud communications
along with the streamline 2-byte command system allow
pins to be changed hundreds of times a second. If the
design requires higher performance than 100s of pin
changes per second the DS3900 may not be a good
choice for that general-purpose bit I/O application.
DS3900
Serial Communications Module
For Evaluation Kits
Troubleshooting
SYMPTOM
CAUSES
SOLUTION(S)
Power might not be applied to the
DS3900, DTR might not be in the correct
state for the DS3900 to operate, the LED
might be connected improperly, or P3
might have been used previously by the
software as an input.
Ensure that power is applied to the circuit and
that DTR is on. Verify that LED is connected
properly. If none of the above works, cycle
power or issue a bit I/O write to P3 to ensure
that P3 is enabled as an output.
The serial cable is not connected, the
DS3900 is not firmly seated on the
application board, power is not applied
to DS3900, or another piece of software
is controlling the serial port.
Make sure the serial cable is connected from
the PC to the DS3900’s DB9 connector. If
multiple serial ports are present on the back of
the PC, ensure the proper port has been
connected. Ensure the DS3900 is well seated
on the application board and that power has
been applied. Check for other software that
may be controlling the serial port.
2-wire communication errors
or general communication errors
Either the PC cannot communicate with
the DS3900, or the DS3900 cannot
communicate with the 2-wire device.
Verify the DS3900 is not held in reset by the
DTR signal. Verify the pullups for SDA and
SCL are on if the application board does not
have pullups. Verify the 2-wire device is being
addressed correctly by the software. Verify
power is applied to the both the DS3900 and
the 2-wire device. Verify the serial cable is
properly connected from the PC to the
DS3900. Verify the DS3900 is properly seated
on the application board.
SDA or SCL line is stuck low
If only SDA is held low, the 2-wire bus
might have been disturbed while a slave
was controlling the bus during a read
operation. Additionally, P10 and P11
may have been used as bit I/O pins and
the last program left the pins in a low
state.
Try to issue a bit I/O read command to the pin
that is stuck low, and the bus will be freed by
the DS3900. If SDA remains low, a slave
device is controlling it. Reset the 2-wire bus
(clock the bus nine times, and issue a stop
command) or cycle power to the application
board to free the pin.
Bit I/O operation not working as
expected
P3 is being used, and the pulse function
is operating and changing the state of
the pin.
Disable the pulse with software, or do not use
P3 for an input or output.
Pulse function not operating properly
DS3900 not found by software after
reset
For technical support email [email protected].
10
____________________________________________________________________
Serial Communications Module
For Evaluation Kits
DS3900
VCC
VCC
4.7kΩ
2.2kΩ
MA2YD15
JP1
P1
CT2192MST
RA2
RA1
RA3
RA0
RA4
MCLR
OSC1
P3
VSS
OSC2
(N.C.) RESET
VSS
GND
P5
GND
JP2
CTX501
P2
P4
4.7kΩ
U1
PIC16LF628
(TSSOP)
VCC
RB0
VCC
RB1
RB7
RB2
RB6
P11-SDA
27pF
P10-SCL
GND
CRYSTAL
3.68MHz
VCC
VCC
27pF
P9
P8
1.0µF
0.1µF
P7
P6
RB5
2 x 8 FEMALE
HEADER
RB3
RB4
VCC
1µF
FORCEOFF
EN
0.1µF
C1+
VCC
V+
GND
C1C2+
1µF
C2V1µF
U2
MAX3223
(SSOP)
T1OUT
R1IN
R1OUT
FORCEON
T2OUT
T1IN
R2IN
T2IN
R2OUT
2 x 8 FEMALE
HEADER
0.1µF
JP3
1
6
2
3
7
8
4
9
5
DB9
INVALID
Figure 2. DS3900 Schematic
____________________________________________________________________
11
DS3900
Serial Communications Module
For Evaluation Kits
TOP LAYOUT
P1
P11
P2
P10
P3
GND
(N.C.) RESET
VCC
GND
P9
P4
P8
P5
P7
GND
P6
BOTTOM LAYOUT
Figure 3. DS3900 Layout
12
____________________________________________________________________
Serial Communications Module
For Evaluation Kits
DS3900
1.344"
X1
C6
C5
C1
JP1
1.584"
C4
U1
1.469"
DS3900 R1.0
SCL
R2
SDA
R3
JP2
1.300"
0.75"
0.84"
0.550"
0.43"
0.312"
0.312"
0.25"
0.100"
0.100"
0.025"
0.25"
0.43"
0.20"
0.025"
1.200"
0.84"
1.56"
1.12"
0.80"
Figure 4. DS3900 Dimensions
Note: The DS3900 mates with standard 2.54mm (0.100in) 2 x 8 male header connectors. These connectors do not
come standard with the board (see Figure 5).
____________________________________________________________________
13
DS3900
Serial Communications Module
For Evaluation Kits
0.100"
0.025", 16 places
0.025"
16 places
0.100"
8 places
0.240",16 places
1.200"
Figure 5. Recommended PC Board Connection for DS3900
14
____________________________________________________________________
Serial Communications Module
For Evaluation Kits
OSCILLATOR
OUTPUTS
PC
OUT1
SCL
OUT0
VCC
SDA
CTRL1
DS1077
GND
SERIAL
PORT
VCC
P1
LED P2
DB9
VCC
P11-SDA
MORE 2-WIRE
DEVICES
P10-SCL
P3
GND
N.C.
VCC
GND
CTRL0
DS3900
P4
P9
P8
P5
P7
GND
P6
VCC
10µF
SDA
VCC
SCL
H0
A0
A1
A2
WP
GND
DS1848
N.C.
H1
L1
N.C.
VARIABLE
RESISTORS
L0
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are
implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 ____________________ 15
© 2004 Maxim Integrated Products
Printed USA
is a registered trademark of Dallas Semiconductor Corporation.
is a registered trademark of Maxim Integrated Products.
DS3900
Typical Operating Circuit