USB RFID Reader Setup: Keyboard Emulation and Card Number Formats

Most USB RFID readers need no software at all: in keyboard-emulation mode the reader types the card number into whatever field has the cursor, usually followed by Enter. What does need setting up is the number format (decimal, 8H10D, Wiegand 26, hex or reversed bytes), which must match what your attendance, POS or access control database already stores. This guide explains the three USB modes, compares the common formats with worked examples, and covers setup and troubleshooting on each operating system.

Keyboard wedge vs virtual COM vs PC/SC

A USB reader presents itself to the computer as a standard USB device class, and that class decides what software you need. USB desktop RFID readers are usually built in one of three ways, and some models can switch between them.

Keyboard emulation (HID keyboard, “keyboard wedge”). The reader enumerates as a USB keyboard. When a card is presented, it sends the card number as keystrokes, typically followed by Enter. There is no driver to install, and it works with any program that accepts typed text, including web forms and spreadsheets. The trade-offs are that data flows one way only, a text field must have focus, and the characters that appear depend on the computer’s keyboard layout. See keyboard emulation in the glossary.

Virtual COM port (USB CDC or USB-serial). The reader appears as a serial port. Your software opens the port and reads each card as a line of text or as a binary frame defined by the reader’s protocol. Because no focused text field is involved, a background service can capture reads while the user works in other windows. The link is two-way, so software can also drive the buzzer and LED or, on reader/writers, write to tags.

PC/SC (USB CCID smart-card class). The reader appears as a smart-card reader, and applications talk to it through the operating system’s PC/SC interface by sending APDU commands. The standard PC/SC “Get Data” command (FF CA 00 00 00) returns the card UID. Depending on the reader and card, the application can also authenticate and read MIFARE Classic sectors, DESFire files or NTAG pages. PC/SC readers are mostly 13.56 MHz devices.

Mode	Appears to the OS as	Driver needed	Data direction	Needs a focused text field	Best for
Keyboard emulation	USB keyboard	No (built in)	Reader to PC only	Yes	Enrollment desks, attendance, POS lookups
Virtual COM	Serial port (COM, /dev/tty*)	Built in for CDC; bridge chips may need one	Two-way	No	Kiosks, background services, reader control
PC/SC (CCID)	Smart-card reader	Built in on Windows and macOS; pcsc-lite on Linux	Two-way, APDU commands	No	Secure card reads, card memory, encoding

Why the typed number differs from the number printed on the card

The chip stores a binary ID. The number printed on the card is one conversion of that ID, chosen by whoever printed the card, and the number your reader types is another conversion, chosen by its output setting. When they differ, one of these is usually the reason:

1. A different slice of the ID. A 125 kHz EM4100 card carries a 40-bit ID. Printed numbers and reader outputs may use all 40 bits, the low 32 bits or only the low 24 bits.
2. Hex versus decimal. 1A7BB26E and 0444314222 are the same 32-bit value.
3. Byte order. A 13.56 MHz UID is a string of bytes. Some readers type it in the order the card transmits it, others reverse it, and the decimal result changes completely.
4. Leading zeros. Some readers pad every number to a fixed length and others do not. 0444314222 and 444314222 are equal as numbers but not as text.
5. UID length. ISO/IEC 14443 UIDs can be 4, 7 or 10 bytes. A 7-byte UID is 14 hex digits, or up to 17 decimal digits, and a reader set to a 10-digit output cannot show it in full.
6. A printed number unrelated to the chip. Some card suppliers print a sequence number rather than a conversion of the chip ID. When you order RFID cards and key fobs, specify which conversion to print.
7. A random UID. Phones emulating a card usually present a random UID, and some cards can be configured to do the same for privacy. The number can change from one tap to the next because the credential is designed that way.

Card number formats compared: decimal, 8H10D, Wiegand 26, hex and reversed bytes

The table shows two example credentials. The first is a 125 kHz EM4100 card with the 40-bit ID 3C1A7BB26E. The second is a 13.56 MHz card with the 4-byte UID A1 B2 C3 D4, listed in the order the card sends it. Format labels vary between readers, so match by the example values rather than by name.

Output setting (common labels)	What the reader types	EM4100 example	13.56 MHz UID example	Length typed
Hex, full ID (10H)	Every ID byte as hex	3C1A7BB26E	A1B2C3D4	10 or 8 characters
Hex, reversed bytes	Byte order swapped, then hex	6EB27B1A (low 4 bytes)	D4C3B2A1	8 characters
Decimal of full ID (10H13D)	All 40 bits as decimal	0258142351982	Same as 8H10D for a 4-byte UID	13 digits
8H10D	Low 32 bits as decimal, zero-padded	0444314222	2712847316	10 digits
8H10D, reversed bytes	Low 4 bytes swapped, then decimal	1857190682	3569595041	10 digits
6H8D	Low 24 bits as decimal	08106606	Depends on which 3 bytes the reader keeps	8 digits
Wiegand 26 style (FFF,CCCCC)	8-bit facility code + 16-bit card number	123,45678 (often typed 12345678)	Depends on which 3 bytes the reader keeps	8 digits
Wiegand 34 style	Two 16-bit halves of the low 32 bits, in decimal	6779 and 45678	Depends on reader	Varies by reader

Three rules come out of the table:

• The 10-digit number printed on many EM cards is usually 8H10D. Set the USB reader to 8H10D when your software stores that number.
• The “123,45678” style printed number is the Wiegand 26 facility code and card number. You cannot recover the 10-digit number from it, because 26-bit output drops the top 8 bits of the 32-bit ID.
• Neither byte order is “correct” for 13.56 MHz UIDs. Readers and software simply differ, so compare one known card on both systems.

For the bit layout behind the Wiegand columns, and a calculator for converting between them, see the Wiegand 26-bit format guide.

Setup on Windows, macOS, Linux and Android

Start the same way on every system: plug the reader in, open a plain text editor, click inside it and present a card. If a number appears followed by a new line, the reader is working in keyboard mode. Everything after that is format and software configuration.

Windows. A keyboard-mode reader appears under Keyboards and Human Interface Devices in Device Manager. A virtual COM reader appears under Ports (COM & LPT); note the COM number and set the baud rate and frame settings from the reader’s datasheet. A PC/SC reader appears under Smart card readers and relies on the Windows Smart Card service. Many reader configuration utilities run only on Windows, so it can be easier to set the output format on a Windows PC before deploying the reader elsewhere.

macOS. When a keyboard-mode reader is first connected, macOS may open the Keyboard Setup Assistant and ask you to press a key the reader cannot press. Close the assistant; the reader still types. Virtual COM readers usually show up as /dev/cu.usbmodem… (CDC class) or /dev/cu.usbserial-… (bridge chip); the exact name depends on the chip. PC/SC readers work through the built-in smart-card framework.

Linux. Keyboard-mode readers work in desktop sessions and on the text console with no setup. For a kiosk that must capture reads without a focused window, read the device’s /dev/input/event* node and grab it so keystrokes do not leak into other applications. Virtual COM readers appear as /dev/ttyACM0 (CDC) or /dev/ttyUSB0 (bridge chip); on Debian and Ubuntu, add the user to the dialout group to open the port. For PC/SC, install the pcsc-lite daemon and the CCID driver package, then confirm detection with pcsc_scan from pcsc-tools.

Android. Connect through a USB OTG adapter or a USB-C port on a device that supports USB host mode, and check that it can supply the reader’s current. A keyboard-mode reader types into the focused field. Android may hide the on-screen keyboard while a hardware keyboard is connected; re-enable it in the keyboard settings if users also need to type. Virtual COM and PC/SC readers need an app that includes its own USB communication code.

iPads with USB-C generally accept keyboard-mode readers the same way; test with your app before rolling out.

Integrating with attendance, POS and access software

Access control enrollment. A desktop reader at the admin desk saves walking every new card to a door. It must type the same number the controller stores: if the panel shows a facility code and card number, use Wiegand 26 output; if it stores a 32-bit decimal, use 8H10D. The door reader and the desktop reader must also read the same card technology; our guide to 125 kHz vs 13.56 MHz covers that choice.

Time attendance and visitor kiosks. Many attendance screens treat Enter as “submit,” so leave the Enter suffix on. For unattended kiosks, a virtual COM reader and a background service avoid the risk of a pop-up window stealing focus and swallowing the number.

POS, membership, loyalty and library systems. Store card numbers as text, not integers, so leading zeros and long 7-byte UIDs survive. Fix one output length and case for the whole site, and make the lookup field accept exactly that.

Web applications. Keyboard-mode readers type into browser forms like any keyboard. Chromium-based desktop browsers can also read virtual COM readers through the Web Serial API after the user grants permission.

UHF desktop readers. Desktop UHF reader/writers used for windshield-tag enrollment often type the EPC in hex, which is 24 characters for a standard 96-bit EPC. The same rules on focus, suffix and text storage apply.

Security. A UID typed by a keyboard-mode reader is an identifier, not proof that the card is genuine. 125 kHz IDs and many 13.56 MHz UIDs can be copied to a writable card. Where cards carry stored value, payments or high-security access, read an authenticated sector or application through PC/SC instead; MIFARE Classic vs DESFire explains the options.

Troubleshooting: leading zeros, Enter suffix, keyboard layout

Symptom	Likely cause	Fix
Leading zeros missing	Spreadsheet or numeric field strips them	Format the column or field as text; use fixed-length output
Long numbers end in zeros in a spreadsheet	Spreadsheets keep about 15 significant digits	Format cells as text before reading 7-byte UIDs
Form submits twice, or not at all	Enter suffix does not match the software	Set the suffix to Enter, Tab or none
Symbols instead of digits, or Q instead of A	Non-US keyboard layout such as French AZERTY	Switch the input layout, use numeric-keypad output or use COM mode
Missing or jumbled characters	Keystrokes too fast for the app or a remote-desktop session	Slow the keystroke rate if configurable; run the app locally or use COM mode
Hex letters change case	Caps Lock is on	Compare card numbers case-insensitively
Reader beeps but nothing appears	No text field has focus, or a Chinese, Japanese or Korean input method (IME) is active	Click into the field; switch to direct input
No beep at all	Card technology not supported by the reader	Check frequency and chip; consider a dual-frequency reader
Different number on every tap	Random UID from a phone or privacy-mode card	Enroll a different identifier, such as a secure application ID
Card reads repeatedly while resting on reader	Continuous read mode	Set single-read mode or a repeat delay

Keyboard layout is the least obvious cause on this list. A keyboard-mode reader sends key positions, not characters, and the computer maps them through its active layout. On AZERTY the digit row needs Shift, so an unshifted “1” appears as “&”, and the key where US layouts have A produces Q.

Checklist before you order a USB reader

• Card technology and frequency: 125 kHz EM or Prox-compatible, 13.56 MHz MIFARE, NTAG or DESFire, or UHF EPC Gen2
• USB mode: keyboard emulation, virtual COM or PC/SC, or a model that switches between them
• One sample card number exactly as your existing system stores it
• Output format that reproduces it, including byte order, hex case and leading zeros
• Suffix and prefix: Enter, Tab or none
• Keyboard layouts and languages of every PC that will use the reader
• Operating systems, plus USB OTG support and power on any tablets
• Read-only, or read/write for encoding cards and tags
• How the format is configured (utility, configuration card or preset before dispatch)
• Cable length and connector (USB-A or USB-C); USB 2.0 cables are limited to 5 m (16 ft) without extenders

Next steps

Send us one card number as your software shows it, the card type, and the operating systems you use. We will confirm which reader and output setting reproduce that number, preset the format before dispatch where the model allows, and ship a sample for testing at your enrollment desk. Request a quote or sample and we will reply within 24 hours.