Why is the number on the card not the number in the platform?
A card stores one code. The printed number, the reader output and the platform field each show it in a different way: hex or decimal, whole or in part, first byte first or last byte first. When two of them disagree, the driver is not recognized and nobody knows why.
| Medium | How it is read | Built-in check | Forms you meet |
|---|---|---|---|
| 125 kHz card (EM4100) | Held near the reader, no contact | Row and column parity | 10 hex digits, decimal of the last 4 bytes, facility and number |
| Wiegand 26 reader output | The reader sends 26 bits to the controller | Two parity bits | Facility and card, 24-bit hex, 26 bits |
| iButton key (1-Wire) | Touched to a contact | CRC-8 | 16 hex digits, 12-digit serial on the key, 64-bit decimal |
This converter takes the number in the form you have and shows every other form of the same code. It also checks the bits that guard against a misread: parity for the two card types and a CRC byte for the key.
How is an EM4100 card built?
The card repeats a 64-bit frame. Forty of those bits are the ID: one version or customer byte and a 32-bit data value. The rest are the header, parity and stop bit.
| Part | Bits | What it holds |
|---|---|---|
| Header | 9 | Nine ones. They mark the start of a frame. |
| Ten rows | 50 | Each row is 4 data bits and 1 even parity bit. |
| Column parity | 4 | One even parity bit for each data column. |
| Stop bit | 1 | Always 0. |
The worked example is the one published with the protocol description: version 06, data 001259E3. Readers often print the last 4 bytes as a 10-digit decimal.
Many readers send an EM card to a Wiegand 26 controller by taking byte 3 as the facility code and bytes 4 and 5 as the card number. EM4100 itself does not define this split. Test one card on your reader before you rely on it.
How does Wiegand 26 work?
A Wiegand reader sends the card data to the controller as 26 bits: a parity bit, an 8-bit facility code, a 16-bit card number and a second parity bit. Each parity bit guards half of the 24 data bits.
| Bit | Meaning | Range |
|---|---|---|
| 1 | Leading parity, even, over bits 2 to 13 | 0 / 1 |
| 2-9 | Facility code | 0 - 255 |
| 10-25 | Card number | 0 - 65535 |
| 26 | Trailing parity, odd, over bits 14 to 25 | 0 / 1 |
Other Wiegand formats, such as 34 or 37 bits, use other layouts. This tool covers the 26-bit format. The parity convention is a choice because readers differ.
What is inside an iButton key?
A 1-Wire key sends 8 bytes when you touch it: a family code, a 48-bit serial number and a CRC-8 byte. The key sends the least significant byte first, so the family code comes first and the CRC last.
| Byte | Meaning |
|---|---|
| 1 | Family code. Many driver keys use 01. |
| 2-7 | 48-bit serial number, least significant byte first |
| 8 | CRC-8 of the first 7 bytes |
Some tools print the 64-bit number the other way round, CRC byte first. If the CRC check fails, try the other byte order before you decide that the key is bad.
How do you enrol many drivers without a mismatch?
- Read one card. Use the reader you will install. Note the form it shows: hex, decimal or facility and number.
- Find the form your platform wants. Check the device manual or the platform help for the driver-ID field. Do not guess the byte order.
- Convert the whole list. Use the list tab. Fix the lines marked as wrong and remove repeats.
- Test with one real card. Enter one driver, swipe the card, and confirm that the right name appears.
- Keep the list. Save the converted list with the installation record, so the next technician can trace any card.
Assumptions and limits
- The tool converts numbers. It does not read cards and it does not know which form your device or platform expects.
- Parity and CRC show that a read was clean. They do not show that a card belongs to a driver or that it is allowed to open anything.
- The facility and number split of an EM card is a common convention. Your reader may use another one.
- The Wiegand parity convention is a setting. The common one is leading even, trailing odd. Check your reader documentation.
- Long numbers are converted with exact digit arithmetic, so a 64-bit value is never rounded.
- The calculations run in your browser. Pasted lists and inputs are sent to our server, and kept for up to 45 days, only if you ask for the emailed report. A share link that you copy yourself also carries a list when it is short.