DS3900 MAXIM | Alldatasheet
Document overview
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Technical content
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 ♦ Connection to Standard Prototyping Boards Possible Using Header Connectors ♦ Operates from 3.0V to 5.5V DS3900 Serial Communications Module For Evaluation Kits
Ordering Information
Rev 1; 7/04 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. Typical Operating Circuit appears at end of data sheet. PART DESCRIPTION DS3900EVKIT DS3900 Module DS3900 Photo R1.0 SCL SDAJP1 JP2 (N.C.) RESET GND GND P11 / SDA P10 / SCL GND VCC DS3900 Pin Configuration
Serial Communications Module For Evaluation Kits RECOMMENDED OPERATING CHARACTERISTICS (VCC = 3.0V to 5.5V, TA = +25°C.) PARAMETER SYMBOL CONDITION MIN TYP MAX UNITS Supply Voltage V CC (Note 1) +3.0 +5.5 V Input Logic 0 V IL (Note 2) 0 0.15 x VCC V Input Logic 1 V IH (Note 2) 0.8 x VCC VCC V Supply Current I CC VCC = 5V 5.0 mA RS232 Baud Rate 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 FUNCTION P1, P2, P4 TO P9 General-purpose bit I/O with tristate I/O pin (input, totem-pole output driver) 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.) 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
sal asynchronous receiver transmitter. the serial port that allows the PC to detect its presence. connected to the reset signal of the microprocessor. connected so it can be controlled through software. state if they are not being driven by external signals.
8 GENERAL-PURPOSE
Figure 1. Functional Diagram
Serial Communications Module For Evaluation Kits Integral Pullups section). This connects 4.7k Ω 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) Place the mating connectors on the circuit board (see Figure 5). 2) Connect V CC and all three ground terminals. 3) Connect the SCL bus to pin P10, and the SDA bus to P11 of the DS3900. 4) 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. 5) Optional: connect an LED to P3 for the pulse func- tion (see Typical Operating Circuit). 6) 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). Designing Hardware to Utilize the General- Purpose 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 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) Place the mating connectors on the circuit board (see Recommended PC Board Connection). 2) Connect V CC and all three GND ground terminals. 3) 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. 4) Optional: connect an LED to P3 for the pulse func- tion (see Typical Operating Circuit). 5) Write software to allow the DS3900 to communi- cate 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 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. DS3900 Revisions 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.
Table 1. DS3900 Command Protocol *See Using the DS3900 with 2-Wire Devices section. **See Using the DS3900's General-Purpose Bit I/O Signals section.
address, and the stop commands. code. If an error occurs, the DS3900 will return 0xFA. For a complete listing of commands see Table 1. (0xA5); Packet Write (0x8%); and Packet Read (0x9%). of 0xB5, and if an error occurs, 0xFA will be returned. values will result in communication problems. Table 2. Bit I/O Addresses Table 3. DS3900 Revisions
- Send a 2-wire Start condition.
- Write the device address R/
using Set Packet Device Address).
- Write the memory address (0x20).
- Write data 0x45 (to address 0x20).
- Write data 0x67 (to address 0x21).
- Write data 0x89 (to address 0x22).
- Send a 2-wire Stop condition.
- If the 2-wire device acknowledges all bytes of the
otherwise it will return an error code (0xFA). edge all but the last data byte sent from the 2-wire part.
- Send a 2-wire Start command.
- Write the device address R/ W =0 (set previously
using Set Packet Device Address).
- Write the memory address 0x20.
- Send a 2-wire Start command (repeated-start).
- Write the device address R/ W =1 (set previously
using Set Packet Device Address).
- Read the data (at address 0x20), send 2-wire
- Read the data (at address 0x21), send 2-wire Not
Table 4. Example of Writing to a DS1803
- Send a 2-wire Stop command.
- If the transmission occurred without errors detect-
else return the error code (0xFA). the slave is holding SDA low. output, and the pulse will begin at the slow rate. Table 5. Example of Reading from a DS1803
Serial Communications Module For Evaluation Kits is tristated and the input is read. The pin remains in a high-impedance state until a write operation is per- formed. 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.
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 con- nects 4.7k Ω 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 appli- cation board’s pullup on at the same time could poten- tially 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 dri- ven 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 manufac- tures 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 pro- vided “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 non- infringement. 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.
Serial Communications Module For Evaluation Kits SYMPTOM CAUSES SOLUTION(S) Pulse function not operating properly 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. DS3900 not found by software after reset 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. Troubleshooting For technical support email MixedSignal.Apps@dalsemi.com.
Figure 2. DS3900 Schematic
Figure 3. DS3900 Layout
Figure 4. DS3900 Dimensions come standard with the board (see Figure 5).
Figure 5. Recommended PC Board Connection for DS3900
Serial Communications Module For Evaluation Kits Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circu it 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 Maxim Integrated Products. is a registered trademark of Dallas Semiconductor Corporation. PC DS3900 DS1848 DS1077 DB9 SERIAL PORT LED VCC 10µF N.C. GND GND P11-SDA P10-SCL GND SDA GND CTRL0 CTRL1 SDA SCL SCL WP GND V CC VARIABLE RESISTORS MORE 2-WIRE DEVICES OSCILLATOR OUTPUTS N.C. N.C. VCC VCC VCC VCC OUT0 OUT1 Typical Operating Circuit