Silicon Laboratories SI2493/57/34/15/04 - Manual (Page 242)

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242 Rev. 1.3
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 V
DD
(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.