How to Bypass M isprogrammed EEPRO M that is Hanging Y our S ystem Application Note TITLE: How to bypass misprogrammed EEPROM that is hanging your system. KEYWORDS: Am79C961, Am79C961A, Am79C965, Am79C970, Am79C970A, EEPROM. PRODUCT: All PCnet controllers with serial configuration EEPROM. VERSION: All silicon revisions. CROSS REF: none SYNOPSIS: If the EEPROM contents is accidentally misprogrammed, it's possible to see strange system behavior including a system hang. You then find yourself in a dilemma where you need to start the system so you can reprogram the EEPROM but you can't because the system hangs with the PCnet adapter card plugged in. This Application Note takes you through the steps necessary to bypass a misprogrammed EEPROM and allow your system to load without hanging. Publication# 21619 Rev. A Amendment/0 Issue Date: March 1995 1 Introduction Most of the PCnet family Ethernet controllers support a serial configuration EEPROM. The EEPROM may be a DIP or a surface mount device, but in either case, it's external to the PCnet controller. At power-on and hardware reset, the PCnet controller automatically senses the presence of the EEPROM and reads the contents into internal configuration and control registers. When programmed correctly, the configuration EEPROM feature is great because your controller automatically initializes itself on power-on and system reset. If the EEPROM contents is accidentally misprogrammed, it's possible to see strange system behavior including a system hang. This can occur because some of the internal control registers control activity on the bus interface. If you load these registers with illogical values, you might cause the controller to grab the bus and prevent other bus activity. When this occurs, you find that you need to restart the system so you can reprogram the EEPROM but you can't because the system hangs with the offending PCnet adapter card plugged in. Bypassing the EEPROM There's a neat little trick you can perform to shut off the PCnet controller and regain control of the system so you can reprogram the serial EEPROM. During the power-on or hardware reset, you simply need to force the controller to think it's detected an EEPROM checksum error while reading the EEPROM. A checksum error will cause the controller to enter a special sleep mode where it's quiescent on the bus. When you run one of the EEPROM programming utilities (e.g. EESETUP or Aminstal), they know how to wake up the controller and perform the EEPROM programming operation. Magic Shorting Step While the system is being powered on or a hardware reset is being applied, short pins 4 and 5 of the serial EEPROM. What you're doing is shorting the EEPROM data out pin (DO) to ground causing the data to look like a bunch of zeros. The bottom line is that the CRC check will fail and the controller will go off into it's quiescent state. For AMD adapter card designs, the EEPROMs used are 93C57, 93C56, and 93C46. These EEPROMs are MICROWIRE compatible, physically compatible with the pin shorting directions given, and are compatible with the EEPROM programming software supplied by AMD. ___ ___ CS | 1 |_| 8 | SK | 2 7 | DI | 3 6 | DO |4 5 | --------- Vcc No Connect ORG (x16) GND Table 1. Serial EEPROM Pin Configuration 2 How to Bypass Misprogrammed EEPROM that is Hanging Your System REFERENCES: Ethernet/IEEE 802.3 Family 1994 World Network Data Book/Handbook Publication ID. 14287C Advanced Micro Devices, Inc. AMD Literature: 1-800-222-9323 Am79C961A PCnet-ISA II Jumperless, Full Duplex Single-Chip Ethernet Controller for ISA data sheet. Publication ID. 19364 Rev.A October 1994 Advanced Micro Devices, Inc. /* End of Application Note: AN901001.TXT */ How to Bypass Misprogrammed EEPROM that is Hanging Your System 3 Trademarks Copyright © 1998 Advanced Micro Devices, Inc. All rights reserved. AMD, the AMD logo, and combinations thereof are trademarks of Advanced Micro Devices, Inc. Am186, Am386, Am486, Am29000, bIMR, eIMR, eIMR+, GigaPHY, HIMIB, ILACC, IMR, IMR+, IMR2, ISA-HUB, MACE, Magic Packet, PCnet, PCnet-FAST, PCnet-FAST+, PCnet-Mobile, QFEX, QFEXr, QuASI, QuEST, QuIET, TAXIchip, TPEX, and TPEX Plus are trademarks of Advanced Micro Devices, Inc. Microsoft is a registered trademark of Microsoft Corporation. Product names used in this publication are for identification purposes only and may be trademarks of their respective companies.