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Issue #208 November 2007
Analog Techniques
iEthernet Bootcamp
Get Started with the W5100
by Fred Eady
Start | WIZnet W5100 | Build A Development Board | WIZnet W5100 Garage Code| Congratulations! | Sources & PDF
BUILD A DEVELOPMENT BOARD
For your convenience, I am supplying the PCB layout for an EDTP Electronics-designed W5100 device (see Photo 1). The PCB layout file on the Circuit Cellar FTP site is in ExpressPCB format. I chose ExpressPCB because it is a relatively inexpensive PCB manufacturing service that is available to everyone. ExpressPCB software is free for download, and the quality of ExpressPCB PCBs is excellent. Another plus associated with using ExpressPCB is that you don’t have to design your W5100 PCB from scratch. You can use my ExpressPCB PCB template and modify it to meet your needs. If you already have a favorite PCB CAD program, you can easily port my design to your CAD format using my original drawing as a guide. As you would expect, I haven’t done anything to complicate the W5100 project board design.
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| Photo 1—My WIZnet W5100 development board is based on the Microchip Technology PIC18LF8722. The PIC18LF8722 is hefty enough to enable the selective use of Direct Memory mode, Indirect Memory mode, and SPI mode access to the W5100’s registers and buffer memory. Using the Microchip PIC18LF8722 also puts the powerful set of Microchip development tools at our disposal. |
The EDTP WIZnet W5100 project board is basically a standard PIC18LF8722 configuration that is wired into a basic W5100 configuration. As you can see in Figure 1, the PIC18LF8722 has enough I/O to wire-in the 15-bit W5100 address bus, the 8-bit W5100 data bus, and all of the W5100 control signals (*RD, *WR, *CS, and *INT) with I/O to spare. In addition to wiring in the W5100 in Direct Bus Interface mode (A0:A14 with D0:D7 and control signals), I attached the W5100’s SPI portal and an SPI select pin to the PIC18LF8722’s SPI I/O interface, which enables you to access the W5100’s internals in W5100 SPI mode. Because the W5100’s address lines are all pulled down internally, the Indirect Bus Interface mode of operation, which uses only two of the 15 address lines, all of the eight data lines, and all of the control signals can also be easily implemented with the EDTP WIZnet W5100 design.
All of the PIC18LF8722’s 80 I/O and power lines are pinned out in blocks of 20 pins to standard 0.1" header pads. The PIC18LF8722 is supported by a 20-MHz clock, a Microchip-certified ICSP programming/debugging portal, and a regulation RS-232 port. I did not include any power supply circuitry because a Digi-Key-supplied 3.3-VDC wall wart does a great job powering the W5100 project board and the external programming/debugging hardware.
On the W5100 side of the EDTP W5100 development board, the W5100 is supported by the required 25-MHz crystal and an all-in-one can of magnetics (see Figure 2). I chose to incorporate the U.D. Electronic RDI-125BAG1A pulse transformer for a couple of reasons. First, the RDI-125BAG1A footprint fits exactly into the old packet whacker pulse transformer footprint, for which I already have a time-proven ExpressPCB pad layout. Second, like the old packet whacker mag jack package, the RDI-125BAG1A has a pair of built-in indicator LEDs in addition to a pair of transmit and receive pulse transformers and the required internal terminating resistors. If you’ve ever worked with the EDTP ASIX-based and Microchip-based Ethernet development boards, you’ll notice that the W5100 PHY connections are very similar to the EDTP Electronics ASIX and Microchip ENC29J60 designs.
You may wonder why there are no bypass components on the W5100’s internally generated 1.8-VDC supply. That question was posted on the W5100 online technical support question-and-answer board. The W5100 engineering answer was to follow the path that was set forth by the W5100 reference schematic, which is void of 1.8-VDC supply bypass components.
Because the EDTP WIZnet W5100 project board is designed to help you get your W5100 design up and running quickly, I attached all of the W5100 LED indicator lines to LEDs. The pair of RDI-125BAG1A LEDs is connected to the W5100’s LINKLED and RXLED status indicator I/O pins. I pulled the TXLED, COLLED, FDXLED, and SPDLED indicators out to discrete LEDs, which you can see in Photo 1 hanging above the city of WIZnet W5100 0805 supporting SMT components. I have also provided a jumper to select W5100 SPI mode if you choose to run your W5100 in that manner. The only oddity I need to point out is the 12.3-kW reset resistor pair you see in Figure 2, which is attached to the W5100’s RSET_BG pin. A bird’s-eye view of the W5100 portion of the EDTP WIZnet W5100 development board is in Photo 2.
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| Photo 2—There’s nothing here you can’t handle. With the exception of the 12.3-kW resistor pair, the line of components closest to the W5100 is all filter and bypass components. The PHY components are in the line closest to the pulse transformer. Note the status LEDs and the SPI select jumper at the port and starboard extremes of this photo. |
As you can see, the W5100 hardware is a no-brainer. Before we move on to do some W5100 coding, what you don’t see in Photo 1 is the heartbeat LED I attached to RG4 on the PIC18LF8722. It’s just there as a warm fuzzy to let me know that things are moving on the firmware side. I flash the RG4 LED at a rate of 1 Hz via the PIC18LF8722’s Timer3 interrupt-driven real-time clock code.
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