Rainbow Electronics MAX66120 - Manual (Page 14)

MAX66120
ISO 15693-Compliant 1Kb Memory Fob
14 ______________________________________________________________________________________
REQUEST FLAGS COMMAND
AFI
(NOTE 1)
MASK LENGTH
MASK PATTERN
(NOTE 2)
(1 Byte) 01h (1 Byte) (1 Byte) (Up to 8 Bytes)
Note 1: The AFI byte is transmitted only if the AFI_flag bit is set to 1. The AFI byte, if transmitted, narrows the range of slaves that
qualify for responding to the request.
Note 2: The mask pattern is transmitted only if the selection mask length is not 0. If the mask length is not an integer multiple of 8,
the MSB of the mask pattern must be padded with 0 bits. The LSb of the mask pattern is transmitted first.
RESPONSE FLAGS DSFID UID
00h (1 Byte) (8 Bytes)
Network Function Commands
The command descriptions show the data fields of the
request and response data packets. To create the com-
plete frame, an SOF, 16-bit CRC, and EOF must be
added (see Figure 5). The ISO 15693 standard defines
four network function commands: Inventory, Stay Quiet,
Select, and Reset to Ready. This section describes the
format of the request and response data packets.
Inventory
The Inventory command allows the master to learn the
UIDs and DSFIDs of all slaves in its RF field in an itera-
tive process. It is the only command for which the
Inventory_flag bit must be 1. The Inventory command
uses two command-specific parameters, which are the
mask length and the mask pattern. The mask allows the
master to preselect slaves for responding to the
Inventory command. The LSb of the mask aligns with
the LSb of the slave’s UID. The master can choose not
to use a mask, in which case all slaves qualify, provid-
ed they are not excluded by the AFI criteria (see the
Request Flags section). The maximum mask length is
60 (3Ch, if Nb_slots_flag = 0) or 64 (40h, if
Nb_slots_flag = 1). The mask pattern defines the least
significant bits (as many as specified by the mask
length) that a slave’s UID must match to qualify for
responding to the Inventory command (case
Nb_slots_flag = 1). If the slot counter is used
(Nb_slots_flag = 0), the value of the slot counter
extends the mask pattern at the higher bits for compari-
son to the slave’s UID. The slot counter starts at 0 after
the inventory request frame is transmitted and incre-
ments during the course of the Inventory command with
every subsequent EOF sent by the master. The pro-
cessing of an Inventory command ends when the mas-
ter sends the SOF of a new frame.
Response data for the Inventory command (no error) is
transmitted only if a slave qualifies to respond. In case
of an error in the request, slaves do not respond.
When receiving the Inventory command, the slave
devices in the RF field enter the collision management
sequence. If a slave meets the conditions to respond, it
sends out a response data packet. If multiple slaves
qualify, e.g., AFI, mask, and slot counter are not used,
the response frames collide and are not readable. To
receive readable response frames with the UID and
DSFID, the master must eliminate the collision.
Not knowing the slave population, the master could
begin with a mask length of 0 and activate the slot
counter. By using this method and going through all 16
slots, the master has a chance to receive clean
responses (i.e., the slave is identified) as well as collid-
ing responses. To prevent a slave that has been identi-
fied from further participating in the collision
management sequence, the master transitions it to the
quiet state. Next, the master issues another Inventory
command where the slot number that previously gener-
ated a collision is now used as a 4-bit mask, and runs
again through all 16 slots. If a collision is found, another
inventory command is issued, this time with a mask that
is extended at the higher bits by the slot counter value
that produced the collision. This process is repeated
until all slaves are identified. For a full description of the
Inventory request processing by the slave device and
the timing specifications, refer to ISO 15693 Part 3,
Sections 8 and 9.
Request Data for the Inventory Command
Response Data for the Inventory Command (No Error)