Modifications to Peripheral Board

10/2001

Background

The CS8900A ethernet chip on the peripheral board can not be accessed due to two problems with board writing. This document describes changes I made to overcome these problems.

Modications

#1 Add wire from U14, pin 7 BCS_N(4) to U9, pin 7 CS8900A CHIPSEL#.

The chip select is wired to BCS_N(5) which is not routed through the connector to the peripheral board. I also changed the software to setup and use CS4 to access the ethernet chip.

#2 Add an inverter to fix bus transceiver direction. 1

I added a 74HC04 inverter, wiring power and ground to available locations (I used bypass caps on the board). I added a wire from U3 LCX16245, pin 1 to HC04 pin 2 and U12 LCX32 pin 6 to HC04 pin 1. This inverts READ# and uses it to control T/R1# on the LCX16245, steering it correctly for reads and writes to the CS8900A.

These changes allowed me to use a slightly modified Cerf driver for the 8900A to connect to the ethernet. The chip functioned correctly and the link and activity lights worked as expected. Since no EEPROM was populated on my board the driver code creates a fictitious MAC address. I wrote code to program the EEPROM via the CS8900 if it is populated.