Silicon Laboratories SI2493/57/34/15/04 Testing and Diagnostics, Prototype Bring-Up Si3018/10

AN93

10. Testing and Diagnostics

10.1. Prototype Bring-Up (Si3018/10)

10.1.1. Introduction

This section provides tips for the debugging of initial prototypes. Although most ISOmodem prototype designs function as expected, there is the potential for layout errors, omitted or incorrect components used in the initial assembly run, and host software problems. If the prototype modem does not function correctly, the techniques outlined in this guide will help quickly isolate the problem and get the prototype functioning correctly. A functional ISOModem evaluation board and data sheet and a computer with HyperTerminal are required for some of the troubleshooting steps. It is assumed that the designer has read the data sheet, implemented the reference design using the recommended bill of materials, and carefully followed the layout guidelines presented in "4.4. Layout Guidelines" on page 49. Troubleshooting begins with system-level checks and then proceeds all the way down to the component level. In this chapter, all system-side pin numbers refer to the 24-pin TSSOP package and all line- side pin numbers refer to the 16-pin version.

10.1.2. Visual Inspection

Before troubleshooting, be certain that the circuit boards and components are clean. Carefully wash the boards to remove all solder flux and solder flakes. Inspect the modem circuitry to ensure all components are installed, and inspect all solder joints for incomplete connections, cold solder joints, and solder bridges. Check all polarized components, such as diodes and capacitors, for correct orientation. Thoroughly clean the circuit board after replacing a component or soldering any connection.

Reset the Modem

Make sure the modem is reset after the power and clocks are applied and stable.

10.1.3. Basic Troubleshooting Steps

Check the Power

With power off, use an ohmmeter to verify that the system ground is connected to ISOmodem pin 6. Turn on system power and measure the voltage between pin 5 and pin 6 and between pin 21 and pin 6 on the ISOmodem. In both cases, the voltage should be 3.3 V. If this is not the case, check the power routing. If power is present, go to the next step.

Check the Phone Line

Check the phone line with a manual telephone to be sure that there is a dial tone and that dialing is possible. The dc voltage across Tip and Ring should read approximately 40–52 V with the phone on-hook.

Reset the Modem

Do a manual reset on the modem. Hold ISOmodem pin 12 (RESET) low for at least 5 ms, return to VDD (3.3 V), and wait for at least 300 ms before executing the first AT command.

Check the DTE Setup (UART Mode)

Be sure the DTE (host) serial port is configured the same as the modem. The default condition is eight data bits, no parity-bit, one stop-bit, and a DTE rate of 19.2 kbps.

Check the DTE Connection (UART Mode)

Check the DTE interface connection. Be sure the RTS (ISOmodem pin 8) and CTS (ISOmodem pin 11) signals are low.

Check the Pulldown Configuration Resistors

Check the Modem Configuration

Read back the modem register settings and correct any inconsistencies. The ATS$ command lists the contents of all S registers, and the AT:R command lists the contents of all U registers.

If the problem was not located with these basic troubleshooting steps, it is time to narrow the problem down to the host system (hardware and software), the ISOmodem chip and associated components, or the Si3018/10 and associated components.

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