Specifications

AN93
Rev. 0.9 157
APPENDIX B—PROTOTYPE BRING-UP GUIDE (Si3018/10)
Introduction
This appendix 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 Si2457/34/15URT-EVB and data sheet and
a computer with HyperTerm is required for some of the
troubleshooting steps. It is assumed that the designer
has read the data sheet, used the reference design and
recommended bill of materials, and has carefully
followed the layout guidelines presented in
" Appendix A—ISOmodem® Layout Guidelines
(Si3018/10)" on page 151. The troubleshooting steps
begin with system-level checks and proceed to the
component level.
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, Zener diodes,
and capacitors for correct orientation. Thoroughly clean
the circuit board after replacing a component or
soldering any connections.
Reset the Modem
Be sure the modem is properly reset after power is
applied and stable.
Basic Troubleshooting Steps
 Check Power
With power off, use an ohmmeter to verify that the
system ground is connected to Si2493/57/34/15/04
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 Si2457/34/15. 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 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 Modem
Do a manual reset on the modem. Hold Si2493/57/
34/15/04 pin 12 (RESET) low for 300 ms; return to
V
DD
(3.3 V) in less than 5 ms, and wait for at least
300 ms before executing the first AT command.
 Check DTE Setup
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 DTE Connection
Check the DTE interface connection. Be sure the
RTS (Si2493/57/34/15/04 pin 8) and CTS (Si2493/
57/34/15/04 pin 11) signals are low.
 Check pullup/pulldown configuration resistor.
Check 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
Si2493/57/34/15/04 chip (and associated components),
or the Si3018/10 (and associated components).
AT OK?
The modem responds with an “OK” to the command
“AT<cr>.”
This indicates that the host processor/software is
communicating with the modem controller, and
problems are in one of the following areas:
 Inappropriate Commands
Verify that all AT commands used are supported by
the Si2493/57/34/15/04 and comply with the proper
format. Be sure the command and argument are
correct. Do not mix upper and lower case alpha
characters in an AT command. An AT command
string contains 48 or fewer characters followed by a
carriage return. Command strings greater than 48
characters are ignored.
 Command Timing
The execution time for an AT command is
approximately 200 ms. Execution is complete when
the “OK” is received. Subsequent AT commands
should wait for the “OK” message, which appears