---
title: "writeSingleBlock(requestFlags:blockNumber:dataBlock:completionHandler:)"
framework: corenfc
role: symbol
role_heading: Instance Method
path: "corenfc/nfciso15693tag/writesingleblock(requestflags:blocknumber:datablock:completionhandler:)"
---

# writeSingleBlock(requestFlags:blockNumber:dataBlock:completionHandler:)

Sends the Write Single Block command (0x21 command code), as defined in the ISO 15693-3 specification, to the tag.

## Declaration

```swift
func writeSingleBlock(requestFlags flags: NFCISO15693RequestFlag, blockNumber: UInt8, dataBlock: Data, completionHandler: @escaping @Sendable ((any Error)?) -> Void)
```

```swift
func writeSingleBlock(requestFlags flags: NFCISO15693RequestFlag, blockNumber: UInt8, dataBlock: Data) async throws
```

## See Also

### Sending Single Block Commands

- [readSingleBlock(requestFlags:blockNumber:completionHandler:)](corenfc/nfciso15693tag/readsingleblock(requestflags:blocknumber:completionhandler:).md)
- [lockBlock(requestFlags:blockNumber:completionHandler:)](corenfc/nfciso15693tag/lockblock(requestflags:blocknumber:completionhandler:).md)