DigitalPlatform
commented
3 years ago 这是在网上找到的一个公开的 IPC RFID 标准，可以方便理解和讨论某些知识点：
IPC-RFID-Standard-for-Test-Letters.pdf
Protocol Control Word 的历史
page 15
A user memory indicator (UMI) is held in location 15HEX. Although MB 11 has no encoding for this IPC
test letter standard, the UMI can have one of these two values:
1 if the tag manufacturer sets this to indicated that MB 11 is present on the tag in accordance
with an option introduced in the ISO/IEC 18000-63:2015 edition.
0 if it is calculated directly by the tag, or alternatively by the interrogator to indicate that there is
no encoding in MB 11 in accordance with an option retained in the ISO/IEC 18000-63:2015
edition from earlier editions. 里面说到，虽然本 IPC test letter 标准没有对 MB11 进行编码，但 UMI 是可以包含两种值之一的。应该是 ISO 18000-63:2015 推介的一个选项，2015 以前没有这个功能。值 0 是从更早的标准版本里面延续下来的，这个值表示标签上没有 MB11。这可以解释一些较早的标准里面没有把 15 bit 叫做 UMI 的现象。
NSI 位
page 16
8.4.2 Encoding the AFI
The AFI is encoded as part of the protocol control word in bit locations 18HEX to 1FHEX. It shall be preceded by a '1' in location 17HEX to enable tags encoded to ISO rules to be distinguished from those encoded to GS1 EPC rules. 这里说了，17 bit 用 '1' 表示标签启用 ISO 规则，区别于 GS1/EPC 规则来进行内容编码。这时候 18-1f bit 表示 AFI。
本文谨记录一些学习理解 UHF RFID 标准过程中的知识点。