---
title: "readSingleBlock(requestFlags:blockNumber:completionHandler:)"
framework: corenfc
role: symbol
role_heading: Instance Method
path: "corenfc/nfciso15693tag/readsingleblock(requestflags:blocknumber:completionhandler:)"
---

# readSingleBlock(requestFlags:blockNumber:completionHandler:)

Sends a Read Single Block command (0x20 command code), as defined in the ISO 15693-3 specification, to the tag.

## Declaration

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

```swift
func readSingleBlock(requestFlags flags: NFCISO15693RequestFlag, blockNumber: UInt8) async throws -> Data
```

## Parameters

- `flags`: The request flags. The doc://com.apple.corenfc/documentation/CoreNFC/NFCISO15693RequestFlag/RequestFlagAddress flag is enforced by default. However, using the doc://com.apple.corenfc/documentation/CoreNFC/NFCISO15693RequestFlag/RequestFlagSelect flag disables the doc://com.apple.corenfc/documentation/CoreNFC/NFCISO15693RequestFlag/RequestFlagAddress flag.
- `blockNumber`: The number of the block to read. Blocks are numbered from 0 to 255 inclusively.
- `completionHandler`: A handler that the reader session invokes after the operation completes. The session calls completionHandler on the dispatch queue that you provided when creating the NFCTagReaderSession object. The handler has the following parameters: When the tag responds with a command error, the error’s doc://com.apple.documentation/documentation/Foundation/NSError/userInfo directory contains the doc://com.apple.corenfc/documentation/CoreNFC/NFCISO15693TagResponseErrorKey and the error’s doc://com.apple.documentation/documentation/Foundation/NSError/code property has a value defined in the ISO15693-3 specification.

## Discussion

Discussion This method sends the tag’s identifier with the command.

## See Also

### Sending Single Block Commands

- [writeSingleBlock(requestFlags:blockNumber:dataBlock:completionHandler:)](corenfc/nfciso15693tag/writesingleblock(requestflags:blocknumber:datablock:completionhandler:).md)
- [lockBlock(requestFlags:blockNumber:completionHandler:)](corenfc/nfciso15693tag/lockblock(requestflags:blocknumber:completionhandler:).md)