# W5100 Ethernet shield: specs and pinout

> An Arduino-format shield that adds a wired 10/100 Ethernet port using the WIZnet W5100 chip, plus a micro SD card slot. The chip facts come from the…

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An Arduino-format shield that adds a wired 10/100 Ethernet port using the WIZnet W5100 chip, plus a micro SD card slot. The chip facts come from the WIZnet W5100 datasheet; the signal names come from the official Arduino Ethernet Shield schematic.

Every value cites its sourceChip-level pinout

[Buy on Compoden](https://compoden.com/products/w5100-ethernet-shield-for-arduino-with-micro-sd-slot)

## Specs

| Spec | Value | Source |
|---|---|---|
| Ethernet | 10BaseT/100BaseTX, embedded PHY, auto negotiation, auto MDI/MDIX | source Features, p.5 |
| Chip supply voltage | 3.0 V to 3.6 V (3.3 V operation with 5 V I/O tolerance) | source Features p.5; Section 7 DC Characteristics, p.64 |
| Host interface | Direct bus, indirect bus or SPI; SPI mode 0 only | source Features p.5; revision history Ver. 1.2.6; Section 6.3 |
| Sockets | 4 independent sockets, simultaneous | source Features, p.5 |
| Internal buffer memory | 16 Kbytes for Tx/Rx | source Features, p.5 |
| Hardware protocols | TCP, UDP, ICMP, IPv4, ARP, IGMP, PPPoE, Ethernet; no IP fragmentation | source Features, p.5 |
| Chip input voltage limit | -0.5 V to 5.5 V (5 V tolerant) | source Section 7 Absolute Maximum Ratings, p.64 |
| Chip operating temperature | -40 C to 85 C | source Section 7 Absolute Maximum Ratings, p.64 |
| Shield design (caveat) | Signal names are from the Arduino Ethernet Shield 06 Rev 03 schematic; the stocked shield is a clone not verified to match that design, so check the board you receive | Arduino official documentation Schematic, ARDUINO ETH SHIELD 06 Rev 03 |

## Power

| | Value | Source |
|---|---|---|
| Supply | Shield is powered from the Arduino 5 V; the schematic shows an MC33269ST-3.3 regulator for the 3.3 V rail | Arduino official documentation Schematic, ARDUINO ETH SHIELD 06 Rev 03 |

## Chip pins
These are the pins of the chip on the module, from the chip datasheet. The module's own header may label or expose them differently.

The signal names are from the official Arduino Ethernet Shield 06 Rev 03 schematic. The stocked shield is a W5100 shield with a micro SD slot; it is not confirmed to be the Arduino original, so check the board you receive. The schematic does not label Arduino digital pin numbers; they are not given here.

| Pin | Function | Voltage | Notes | Source |
|---|---|---|---|---|
| SCK | SPI clock | | Shared by the W5100 and the SD card | Arduino official documentation Schematic, header and W5100 SCLK net |
| MOSI | SPI data in | | Shared by the W5100 and the SD card | Arduino official documentation Schematic |
| MISO | SPI data out | | Shared by the W5100 and the SD card | Arduino official documentation Schematic |
| SS | W5100 chip select (/SCS) | | Active low | Arduino official documentation Schematic, W5100 *SCS pin |
| SD_CS | SD card chip select | | Schematic shows 74LVC1G125 buffers on the SD card lines | Arduino official documentation Schematic, SD card socket |
| RESET | Board reset line to the W5100 reset circuit | | Schematic shows a CAT811 reset supervisor (RESET_W) | Arduino official documentation Schematic, power and reset block |

## Build with it
Project ideas for the W5100 Ethernet shield. Each link opens Soldr with the prompt filled in; Soldr assigns the pins, checks power and shows how to wire every part.

- [A local network web page that shows room temperature using an Arduino Uno, a W5100 Ethernet shield and a DHT22 sensor](https://app.soldr.ai/?prompt=I%20want%20to%20build%20a%20local%20network%20web%20page%20that%20shows%20room%20temperature%20using%20an%20Arduino%20Uno%2C%20a%20W5100%20Ethernet%20shield%20and%20a%20DHT22%20sensor): The Uno serves a small web page over the cable; the DHT22 runs from the Uno 5 V. Use the DHT22 in its normal range.
- [SD card sensor logger](https://app.soldr.ai/?prompt=I%20want%20to%20build%20a%20data%20logger%20that%20writes%20readings%20to%20a%20micro%20SD%20card%20and%20serves%20them%20over%20Ethernet%20using%20an%20Arduino%20Uno%2C%20a%20W5100%20Ethernet%20shield%20and%20a%20DS18B20%20sensor): The shield carries the SD slot; keep the SD and Ethernet chip-selects separate by following the library example for the shield (pin numbers are not in the sources). The DS18B20 data line needs its pull-up resistor (take it from the resistor pack; value per the probe's page).
- [LAN LED switch](https://app.soldr.ai/?prompt=I%20want%20to%20build%20a%20web%20page%20that%20switches%20an%20LED%20on%20and%20off%20over%20the%20local%20network%20using%20an%20Arduino%20Uno%20and%20a%20W5100%20Ethernet%20shield): A first Ethernet project: a page with two links toggles one output. Use an LED with a series resistor from the resistor pack, not mains.

## Common mistakes

- The chip supports SPI mode 0 only, not mode 3; keep the SPI settings at the default mode (source: [link](https://docs.wiznet.io/assets/files/W5100_DS_V128E-68b8612e5ec92bb4cdf8f53cf6bfb8a9.pdf), revision history Ver. 1.2.6 and Section 6.3).
- Only 4 sockets can be open at once, and IP fragmentation is not supported: close connections you no longer need and keep packets small (source: [link](https://docs.wiznet.io/assets/files/W5100_DS_V128E-68b8612e5ec92bb4cdf8f53cf6bfb8a9.pdf), Features, p.5).
- The Ethernet chip and the SD card share the SPI bus: only one chip-select may be active at a time. The Arduino schematic shows separate SS and SD_CS lines; pin numbers are not in the sources, so follow the library example for the shield (source: Arduino official documentation schematic).

## Not covered by the official source

- The shield on sale is a W5100 + SD design; whether it is the Arduino original or a clone is not verified.
- Arduino pin numbers used by the shield are not stated in the schematic text and are not given here.
- Shield current draw is not documented in the sources.

## Sources

- [link](https://docs.wiznet.io/assets/files/W5100_DS_V128E-68b8612e5ec92bb4cdf8f53cf6bfb8a9.pdf) (WIZnet W5100 Datasheet Ver. 1.2.8)
- Arduino official documentation (Arduino Ethernet Shield 06 Rev 03 schematic)