19-1306; Rev 0; 3/98 MAXSMBus 2-Wire Interface Board ____________________________Features MAXSMBus is an interface between an IBM-compatible PC and System Management Bus (SMBus™)compatible serial-interface devices such as temperature monitors, voltage regulators, or A/D converters (ADCs). The MAXSMBus interface board is connected between the PC parallel port and the device under test, converting parallel data into 2-wire, open-drain serial data. The board is provided for use with selected Maxim products and is not intended to replace commercially available SMBus hardware. MAXSMBus is shipped with a companion EV kit board, including all relevant software. ♦ SMBus-Compatible 2-Wire Interface Maxim SMBus Interface Board ____________________________Component List DESIGNATION QTY DESCRIPTION C1, C2, C3 3 0.1µF ceramic capacitors C4–C9 6 3.3µF, 25V tantalum capacitors D1 1 1N5235B zener diode, 6.8V D2 1 1N5229B zener diode, 4.3V D3 1 1N4148 small-signal diode J1 1 DB25 right-angle plug J2 1 Not installed P1 1 2x10 right-angle male header R1, R2, R3, R10, R11 5 47kΩ ±5% resistors R4–R7 4 4.7kΩ ±5% resistors R8, R9 2 1kΩ ±5% resistors U1 1 74HC05 hex open-collector inverter U2 1 74HC04 hex inverter U3 1 74HC08 quad AND gate U4 1 74HC74 dual D flip-flop U5 1 +5V, 100mA regulator LM78L05ACM U6 1 MAX865EUA (8-pin µMAX) U7 1 MAX367CWN (18-pin SO) NONE 1 PC board ♦ SMBus Suspend Output ♦ Two SMBus Alert Inputs ♦ Overvoltage Fault Protection ♦ PC Parallel Port Interface _______________Ordering Information PART BOARD TYPE MAXSMBus Companion Board for SMBus EV Kits ___MAXSMBus Functionality Check Follow these steps to verify that the MAXSMBus interface board is functioning properly. All necessary software is supplied on a disk with the companion EV kit. Instructions for operating the software are included in the EV kit manual. 1) Connect a +9VDC supply (+7V minimum, +20V maximum) to the MAXSMBus interface board at the terminals labeled POS9 and GND in the lower left corner of the board. 2) Use a digital voltmeter to verify that the oval pad labeled POS5 is +5V (+4.75V minimum, +5.25V maximum). Also verify that the pads labeled SBDAT1, SBCLK1, SBSUS1, ALERT1, and ALERT2 are above +4V. 3) If these DC voltages are correct, MAXSMBus passes the functionality test. _______________Detailed Description The MAXSMBus interface board provides all of the interface signals necessary to interface an IBM PCcompatible computer with an SMBus-compliant device. A DB25 right-angle plug connects to the computer (Table 1). The companion board plugs into a 20-pin dual-row right-angle header at the edge of the board (Table 2). Alternatively, connection can be made by soldering wires to the oval pads as appropriate. This allows the companion board to be placed in an environmental chamber for evaluation over temperature. Refer to the documentation of the companion Maxim EV kit for quick start and operating instructions. SMBus is a trademark of Intel Corp. ________________________________________________________________ Maxim Integrated Products 1 For free samples and the latest literature, visit www.maxim-ic.com or phone 1-800-998-8800. For small orders, phone 1-800-835-8769. Evaluates: MAXSMBus ________________General Description Evaluates: MAXSMBus MAXSMBus 2-Wire Interface Board Power Supply Bus Driving Circuitry The interface board is powered by a 78L05 linear regulator. The companion board can draw about 20mA of +5V power through the circuit protector. Companion boards that require more power must provide their own regulator. The unregulated input to the 78L05 is available on the right-angle header. A 74HC05 open-drain inverter (U1) is used to pull down the SMBus interface signals. The 74HC08 (U3), 74HC74 (U4), and 74HC04 (U2) buffer the signal to the IBM PC and provide the capability to mask the ALERT interrupts, detect an externally generated start condition, and capture data sent by an external bus master. Interface connections are listed in Table 1 and Table 2. Fault-Protection Circuitry Overvoltage fault protection is provided by a MAX367 fault protector (U7). If any of the SMBus interface signals exceed the MAX367’s power-supply rails, the MAX367 increases its resistance to prevent damage to the user’s computer. A MAX865 dual charge pump (U6) and two zener diodes (D1 and D2) provide +7V and -3V supplies to the MAX367, thus allowing 0V and +5V signals to pass with a nominal resistance of 100Ω. Bus Monitoring Circuitry Flip-flop U4A detects the start condition (falling edge of SMBDATA when SMBCLK is high). Flip-flop U4B detects the falling SMBCLK edge when enabled, and U1F holds SMBCLK low until the software releases it. To advance to the next data bit, the software uses U1A to assert and then release SMBCLK. A logic high at the input of U1A also resets flip-flop U4B. Because the IBM PC parallel port has a limited number of inputs, the start-detect circuit and the two alert inputs share a single interrupt input. The source of the interrupt is distinguished using U3A, U3B, and U3C. ________________________________________________________Troubleshooting Guide SYMPTOM CAUSE Can’t Find the Interface Board Board not connected to parallel printer port Verify that the cable is a 25-pin parallel port I/O extension cable with a plug on one end and a socket on the other end. Verify that the cable is connected to a printer port, not a floppy disk, SCSI, or serial communications port. Clock or Data Stuck Low Board is connected to correct port, but SMBus is not functioning Check power connections on the interface board. Check clock and data signal connections. Try operating the interface board without the companion Maxim evaluation kit—this should cause the address-not-acknowledged symptom described below. SMBus is OK, but no response at expected SMBus address Verify that the companion board is connected to the MAXSMBus interface board. Verify that the companion board is powered. If the companion offers a choice of addresses, confirm that the software and hardware addresses match. Some devices only read the address select pins at device power-up. Conflict with local printer driver Disable print manager in Windows printer control panel. Disable printer driver. Operating system conflict 1) Use computer with commercially available BIOS. 2) Make a bootable floppy disk, remove unnecessary device drivers from A:config.sys, and boot system from floppy. Address Not Acknowledged Erratic Operation 2 SOLUTION _______________________________________________________________________________________ MAXSMBus 2-Wire Interface Board Evaluates: MAXSMBus Table 1. DB25 Connector Signals PIN NAME 1 3 SPARE OUTPUT A SMBCLK_ OUT SMBDATA_ OUT 4 SMBUS_OUT 5 8 LOOPBACK MASK_ ALERT1 MASK_ ALERT2 MASK_ START 9 CAPTURE_ENABLE 10 INT 2 6 7 FUNCTION Spare output When high, drives SMBCLK signal low When high, drives SMBDATA signal low When high, drives SMBSUS signal low Loopback connection for port verification When high, allows ALERT1 to trigger INT low When high, allows ALERT2 to trigger INT low When high, allows a start condition to trigger INT low When high, enables slave / bus monitor circuitry. This circuit waits until SMBCLK is pulled low, and then it holds SMBCLK until the software resets it. Active low interrupt input 12 SMBDATA_ IN SMBCLK_ IN 13 LOOPBACK 14 15 SPARE OUTPUT B HOLDING_ CLOCK 16 UNUSED Not used 17 UNUSED Not used 18–25 GND 11 When high, indicates that SMBDATA is low When high, indicates that SMBCLK is low Loopback connection for port verification Spare output When low, indicates that interface board is holding SMBCLK low Signal ground return _______________________________________________________________________________________ 3 Evaluates: MAXSMBus MAXSMBus 2-Wire Interface Board Table 2. Right-Angle Header P1 Signals PIN NAME FUNCTION 1 DUT +5V 2 GND 3 DUT SDA 4 GND Signal ground return 5 GND Signal ground return 6 GND Signal ground return 7 DUT SCL 8 GND 9 DUTSMBSUS 10 GND 11 DUTSMBALERT 12 GND 13 DUTALERT2 14 GND 15 SPARE OUTPUT A 16 GND 17 SPARE OUTPUT B 18 GND Signal ground return 19 GND Signal ground return 20 RAW POWER +5V at 20mA power supply to Maxim companion board Signal ground return SMBDATA interface signal SMBCLK interface signal Signal ground return SMBSUS interface signal Signal ground return Primary ALERT interface signal Signal ground return Secondary ALERT interface signal Signal ground return Spare output from pin 1 of the DB25 connector Signal ground return Spare output from pin 14 of the DB25 connector Unregulated, unprotected power-supply input to MAXSMBus interface board Note: Odd-numbered pins are on the outer row. Even-numbered pins are on the inner row. All right-angle header signals pass through the MAX367 circuit protector, except 20. 4 _______________________________________________________________________________________ _______________________________________________________________________________________ J1–11 J1–3 J1–12 J1–2 J1–9 GND R7 4.7k SMBDATA_IN R6 4.7k SMBDATA_OUT SMBCLK_IN R5 4.7k SMBCLK_OUT R4 4.7k CAPTURE_ENABLE SMBSUS_DUT J1–4 CAPTURE_ENABLE SMBCLK SMBDATA_IN 8 3 6 1 3 U2B R D 1 74HC04 U2D 74HC05 OC U1B 74HC04 U2C 74HC05 OC U1A Q Q 9 4 5 2 4 ALERT2 +5V 2 SMBSUS 5 START DETECTED 6 11 10 SMBDATA SMBDATA SMBCLK DRIVE_SCL_LOW 13 CAPTURE_ENABLE 12 SMBCLK_IN 74HC04 U2A 74HC74 CLK S 74HC04 1 2 3 4 U4A +5V Q Q R1 47k R2 47k +5V 74HC74 R D CLK S U4B SMBSUS R11 47k R10 47k 9 8 13 11 +5V 12 11 13 SMBDATA SMBCLK 13 74HC08 U3D U3A 4 74HC05 OC U1F 12 10 74HC08 U3C 5 74HC08 U3B 2 74HC08 1 HOLDING_CLOCK J1–15 J1–8 MASK_START 12 ALERT2 ALERT1 START_DETECTED 9 J1–7 MASK_ALERT2 74HC04 U2F J1–6 MASK_ALERT1 74HC04 CAPTURE_ENABLE GRAB_SCL ALERT2 ALERT1 10 9 5 J1–5 74HC05 OC U1E 74HC05 OC U1D 74HC05 OC U1C SMBCLK 8 11 6 3 10 +5V R3 47k INT J1–10 J1–23 J1–24 J1–25 J1–22 J1–21 J1–20 J1–19 J1–18 LOOPBACK C1 0.1µF +5V C2 0.1µF DECOUPLING CAPACITOR GND J1–13 C3 0.1µF SMBCLK_IN J2–12 J2–11 MASK_START CAPTURE_ENABLE INT SMBDATA_IN J2–7 J2–8 J2–9 J2–10 MASK_ALERT1 MASK_ALERT2 J2–5 J2–6 INTERFACE TEST POINTS HOLDING_CLOCK J2–1 SMBCLK_OUT J2–2 SMBDATA_OUT J2–3 SMBSUS_OUT J2–4 8 6 Evaluates: MAXSMBus ALERT1 U2E MAXSMBus 2-Wire Interface Board Figure 1. MAXSMBus Schematic 5 6 +5V Figure 1. MAXSMBus Schematic (continued) _______________________________________________________________________________________ GND1 +5V POS9 -10V J1–1 J1–14 ALERT2 ALERT1 SMBSUS SMBCLK SMBDATA +10V U7 14 13 12 11 10 4 5 6 7 8 8 +9V IN GND 7 GND 6 5 N.C. U5 LM78L05ACM D3 15 3 D2 4.3V 16 2 9 17 MAX367 18 GND 1 D1 6.8V OUT 2 GND 3 GND 4 N.C. 1 R9 1k R8 1k C8 3.3µF 25V +9V +5V C9 3.3µF 25V C5 3.3µF 25V U6 +9V 8 C1V+ 7 IN 6 5 GND C6 3.3µF 25V P1–19 P1–17 P1–15 P1–13 P1–11 P1–9 P1–7 P1–5 P1–3 P1–1 C7 3.3µF 25V -10V GND C4 3.3µF 25V P1–20 P1–18 P1–16 P1–14 P1–12 P1–10 P1–8 P1–6 P1–4 P1–2 P1 2 x 10 RIGHT-ANGLE HEADER MAX865 C1+ 2 C2+ 3 C24 V- 1 SPARE OUTPUT J1–14 SPARE OUTPUT J1–1 DUT ALERT2 DUT SMBALERT DUT SMBSUS DUT SCL DUT SDA DUT +5V GND GND0 ALERT2 ALERT1 SBSUS1 SBCLK1 SBDAT1 POS5 +5V +10V Evaluates: MAXSMBus MAXSMBus 2-Wire Interface Board MAXSMBus 2-Wire Interface Board Evaluates: MAXSMBus 1.0" 1.0" Figure 2. MAXSMBus Component Placement Guide Figure 3. MAXSMBus PC Board Layout—Component Side _______________________________________________________________________________________ 7 Evaluates: MAXSMBus MAXSMBus 2-Wire Interface Board 1.0" Figure 4. MAXSMBus PC Board Layout—Solder Side 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. 8 _____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 © 2000 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.