The Schematic and the PCB

Schematics

This is the schematic (PROTEL file) of our Embedded Ethernet Device board.

The brain of this system is the SCENIX SX52 microcontroller. This one can run at 50mhz (even 100Mhz). To program this device is a real pleasure, since it has a Flash EEPROM program memory, and can be erased in 5 seconds, programmed in 10 seconds. This microcontrollers has a very nice debugger attached to a PC by the RS232 link that can allows to trace all the code instructions : no need of emulator and logical analyser to debug it.It's a very affordable solution. SX52 can run in a standalone mode with a 50Mhz oscillator, or be run by the SX Key clock (JP5 and JP6).

We add to the SX52, 2K of SRAM to store the ethernet frame, because the SX52's memory is not so huge, and sometime one need to send again back the ethernet frame if it has not reached the PC.

The ethernet controller is the Cirrus Logic CS8900, a very powerfull IC which does all the work for you. This kind of circuit is generally installed in PC/ISA board network adapters. The CS8900 can use DMA, has a 20 bit adress bus, 16 Data bus, etc etc... In our case, we use this circuit in a straigthforward mode : using 8 bit data in IO mode. IO mode means that we address the device at $300 with a 4 bit bus, meanning that we can read/write addresses from $300, $301 ... to $30F.

Two FIFOs have been installed, the first one is used to send commands to the slave microcontroller, SX52 can write a batch of commands, the FIFO size could be limited to 512 bytes for that purpose. The other FIFO allows the slave microcontroller to send to the SX52 hand shake and datas.

In the case of the use of a slave microcontroller for reading out CCDs camera, this FIFO must be more than 5K. We choose 16K, to allow continous/in-interrupted CCD readout. It lets time to the SX52 to send data over the LAN, even allowing to re-send data in the case of frame loss/colision without having to stop to readout the CCD : that's a big advantage ! It also makes possible to use Time Delay Integration mode with very accurate pixel readout timming.

The PCB

PCB has been done using PROTEL software, it ended up to a two layer PCB of 101x68mm. The PCB has been manufactured here. SMD parts have been used, and concerning resistor and caps, those are really easy to solder, evne with a . The SX52 is still OK to solder. Nevertheless, the CS8900 has 100 0.5mm spaced pins and is the most difficult part to solder: it requires special tools. So, I strongly recommand you to read this document.

EED 2 layer PCB

Part list

RS= RadioSpare GERMANY

(*) figure rounded to 200 Dm because of the price SMD cap and resistor part is not mentionned here.