Standardisation - RFID: Fundamentals and Applications in Contactless Smart Cards and Identification - page 227

Settling time SWITCH window

ISO 11785 Mode Advanced mode

> 5 ms
off-
time

Reader field

SWITCH
command

Command

Transponder
response

ISO 11785 ID Answer

Figure 9.4 Signal path at the antenna of a reader

Table 9.2 Parameters of the transmission link from reader to transponder (downlinks)

Parameter Mode switching Advanced mode

Modulation procedure ASK 90-100% ASK 90-100%

Coding Binary Pulse Length PIE (Pulse interval encoding)

Baud rate 6000 bit/s (LSB first) 6000 bit/s (LSB first)

Mode switching code 5 bit pattern (00011) —

Mode switching timing Transponder settling time:

312 . 5 / fc = 2 . 33ms
SWITCH window:
232 . 5 / fc = 1 . 73

'SWITCH' command. The transponder then awaits further commands from the reader.
See Figure 9.4.
HDX-ADV A sequential transponder (HDX) charges its charging capacitor during the
50ms period that the field is switched on. Within the 3ms field pause the transponder
begins to transmit the 64-bit identification code, as defined in ISO/IEC 11785. The
duration of the pause is extended to a maximum of 20ms to facilitate the complete
transfer of the data block. An advanced transponder (HDX-ADV) is recognised by the
setting of bit 16 (data block follows) in the identification code.
A sequential transponder can be switched to any interrogation cycle in advanced
mode. To achieve this, a command is simply sent to the transponder in the second half of
the 50ms period in which the field is switched on (Figure 9.5). The transponder executes
this command immediately and sends its response to the reader in the next pause. If no
command is sent in an interrogation cycle, then the transponder automatically reverts
to ISO 11785 mode and transmits its identification code to the reader in the next pause.

9.1.3.2 Part 2 - Codeand commandstructure

This part of the standard describes the simple transmission protocol between transpon-
der and reader, the memory organisation of the transponder, and commands that must
be supported by advanced transponders.