AN2399
Application note
RFID library for SR176 tag management with STR71x
Introduction
This document describes a software and hardware RFID interface using the STR71x I2C
peripheral and the CRX14 RFID transceiver.
The main purpose of this software and hardware package is to provide resources to assist
the development of an application using an RFID tag.
The software interface is composed of library source files, include files and some application
template source files.
January 2008
Rev 1
1/22
www.st.com
Contents
AN2399
Contents
1
File organization of the RFID library . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2
Overview of radio frequency identification . . . . . . . . . . . . . . . . . . . . . . . 4
3
Operating ranges and applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
4
3.1
Close coupling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.2
Short range . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.3
Long range . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.4
Extended or very long range . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
ISO standards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
4.1
5
ISO compatibility for ST devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
ST short-range contactless memories . . . . . . . . . . . . . . . . . . . . . . . . . . 7
5.1
SR176 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
5.2
SRIX4K . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
5.3
SRIX512 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
6
ST short range coupler: CRX14 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
7
Overview of RFID reader using STR710 . . . . . . . . . . . . . . . . . . . . . . . . . 9
8
9
2/22
7.1
CRX14 demonstration kit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
7.2
Interfacing with STR7xx using I2C peripheral . . . . . . . . . . . . . . . . . . . . . 12
RFID library . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
8.1
RFID reader/writer: the application layer . . . . . . . . . . . . . . . . . . . . . . . . . 14
8.2
SR176 commands layer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
8.3
CRX14 commands layer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
8.4
I2C commands layer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
AN2399
1
File organization of the RFID library
File organization of the RFID library
The following table presents the library modules:
Table 1.
RFID library modules
File
Description
Device_RFID.h
RFID definitions, type definitions and function prototypes
Device_RFID.c
Protocol management to interface the CRX14 transceiver
3/22
Overview of radio frequency identification
2
AN2399
Overview of radio frequency identification
Countless business applications, from product manufacturing to end-customer sales, can
benefit from radio frequency identification (RFID). With RFID, logistics becomes more
effective, stock handling is easier, traceability is guaranteed, cloning and counterfeiting can
be avoided, antitheft protection is enabled, and warranty problems can be easily eliminated.
What is radio frequency identification (RFID)?
RFID technology uses radio communications to uniquely identify items, such as goods,
people, or animals. It enables automated collection of information on identified items
independently from their position, without the need of a direct optical link or human
intervention. RFID also liberates the user from harsh or dirty environment concerns that
restrict other automatic identification solutions such as barcodes. On top of that, RFID is
used as a bi-directional data carrier since it allows information attached to the item to be
written and updated on the fly.
What does a RFID system consist of?
An RFID system consists of several components including one or multiple contactless
memory tags (or transponders), attached to the items to be labeled, identified, and traced,
and handheld or fixed contactless read/write reader station units or coupling devices
exchanging data with the transponder(s) by means of RF signals.
Contactless memory tags
Contactless memory tags (transponders) are the backbone of the RFID system since
they contain data that allow the items to be identified. A contactless memory tag is made of
a non-volatile memory associated with a radio frequency communication block, performing
RF signal modulation, demodulation, power supply regulation, and an antenna. A
transponder can be read-only (ROM), one-time-programmable (OTP), or read/write
(EEPROM), and it can be embedded in various package formats (inlays, cards, etc.).
The reader
The reader (or reader station unit) is connected to an antenna that transmits and receives
the radio frequency signal from and to the transponder(s). The reader sends an RF signal to
the transponder’s antenna. This signal generates a voltage that is rectified and provides a
power source to the transponder. The power transfer from the reader to the transponder is
performed through an inductive coupling between the two coils in 125 kHz and 13.56 MHz
systems. For ultra-high frequencies (UHF), the electric field generated by the reader is used
to power the tag. In other words, the transponder does not need a dedicated power supply.
Passive and active tags
Two main families of transponders exist: Passive (battery-less) and Active. Adding a battery
can bring several advantages, such as improvement of the reading range or continuous
monitoring of temperature and pressure etc., but adds an extra cost. During the readertransponder communication, the RF signal generated by the reader is modulated according
to the data to be sent. In the transponder-reader direction, no modulation is applied on the
reader RF signal and the communication is done through load modulation in inductive
coupling systems. The reader interfaces with the RFID system control host through a serial
interface such as RS232, RS422/485, or USB.
4/22
AN2399
3
Operating ranges and applications
Operating ranges and applications
The RFID operating ranges are defined by the distance between the transponder(s) and the
reader.
3.1
Close coupling
The close-coupling range includes the transponder-reader distances up to 5 cm. Brand
protection, anti-counterfeiting of electronic goods and food consumables, as well as
electronic purchases at vending machines operate in the close-coupling range. These
applications employ low-cost readers operating with a limited number of transponders and
require security features such as password, anti-clone, or cryptographic capabilities.
3.2
Short range
In addition, RF technology systems are a universal solution for various ticketing applications,
regardless of the means of transport used (public transportation or private car). Contactless
systems can also be used in a wide range of access-control applications, including entrance
systems to and within public buildings (in offices, for example), time and attendance
systems, room logistics at hotels, locking systems, and amusement parks. These shortrange or proximity-range applications use low-cost transponders embedded in plastic cards
or paper tickets and operate in the range up to 20 cm. Readers and transponders from
different suppliers must be fully interoperable. Required security levels are satisfied through
password, anti-clone, or cryptographic capabilities.
3.3
Long range
RF transponders are a low-cost universal solution for tracking a wide variety of valuable
assets (e.g. package delivery, animal tracking) and improving the product supply chain
management from manufacturing to stock handling to distribution. Capable of storing
traceability history, transponders provide accurate real-time information on each tagged
item. Similarly, they can be used for anti-theft applications (using Electric Article
Surveillance) or access control from a longer distance.
These long-range or vicinity-range applications operate within 1 m from the reader and
typically involve a large number of low-cost transponders (100+), requiring reliable anticollision mechanisms and transponder-reader interoperability.
3.4
Extended or very long range
Extended or very long-range (up to 10 meters) RFID systems will be instrumental in creating
low-cost contactless solutions for new supply chains, logistics, and tracking applications that
can offer improved efficiency, accuracy, and security standards to major manufacturers,
retailers, and their customers.
5/22
ISO standards
4
AN2399
ISO standards
The ISO organization devotes itself to definition and promotion of worldwide-recognized
standards in the contactless area. 3 standards for objects operating in the 13.56 MHz
frequency range have already been approved (ISO SC17 on identification cards and related
devices):
●
ISO10536 identification cards and contactless integrated circuits cards:
–
●
ISO 14443 identification cards and contactless integrated circuits cards:
–
●
Close-coupling cards (reading range below 2 cm).
Proximity cards (reading range up to 20 cm).
ISO 15693 identification cards and contactless integrated circuits cards:
–
Vicinity cards (reading range up to 1 m).
This standard is part of the future SC31/ISO18000 standard, currently under
discussion.
ISO standards are recognized worldwide and guarantee the full interoperability of
transponders and readers from different suppliers.
4.1
ISO compatibility for ST devices
ST contactless memories are ISO-compatible:
●
ISO 14443 type B for short-range devices
●
ISO 15693 or ISO18000-3 Mode 1 for long-range devices.
This application note refers to ST ISO 14443B short range RFID.
6/22
AN2399
ST short-range contactless memories
5
ST short-range contactless memories
5.1
SR176
ST’s SR176 is an ISO14443 Type B device. It offers 176 bits of EEPROM organized in
eleven 16-bit blocks, a 64-bit UID and an 8-bit Chip_ID. Targeted markets are cost-sensitive
applications such as industrial identification, access control, and low-value tickets that do
not need to be modified more than a few times.
5.2
SRIX4K
ST’s SRIX4K includes 4096 bits of non-volatile memory organized in three areas: the first
area is an OTP (One Time Programmable) bit zone, in which bits can only be switched from
1 to 0; the second area provides two 32-bit binary down counters; and the last area which is
a non-volatile memory split into 32-bit blocks (9 blocks are lockable). The SRIX4K supports
France Telecom’s proprietary anti-clone function and anti-collision mechanism based on an
8-bit Chip_ID.
The SRI4K is based on the SRIX4K, excluding the support of France Telecom’s proprietary
anti-clone function.
5.3
SRIX512
The SRIX512 is a light version of the SRIX4K with 512 bits of non-volatile memory. All three
devices (SRIX4K, SRI4K, SRIX512) are designed for short-range applications such as
consumable products identification, anti-counterfeiting, or high-end ticketing solutions.
7/22
ST short range coupler: CRX14
6
AN2399
ST short range coupler: CRX14
The CRX14 is a short-range contactless chip coupler compliant with the ISO14443 type B
standard. It interfaces with the host CPU that manages the communications protocol in both
directions through the industry-standard I²C serial bus. The coupler is equipped with France
Telecom’s proprietary anti-clone function and anti-collision mechanism. The CRX14 is
supplied in SO16N packages.
A complete solution combining the CRX14 coupler and SRxx transponders operates in the
short range and ensures a total compatibility in terms of memory tag protocol access. In
addition, the combination of the CRX14 and SRIX512 or SRIX4K memories guarantees a
high level of system security for short-range and low-cost applications. Optimized for
interoperability, these products can also work independently, with any ISO-standard chips.
The CR14 is based on the CRX14, excluding the support of France Telecom’s proprietary
anti-clone function.
8/22
AN2399
7
Overview of RFID reader using STR710
Overview of RFID reader using STR710
The RFID reader is developed using the STR710 ARM7TDMI powered microcontroller and
the CRX14 low cost contactless coupler chip. Communication between the microcontroller
and the coupler is achieved by an I2C bus.
The RFID library has been developed to support SR176 tag.
As depicted in picture below, the RFID library has been developed on a 4-layer structure.
Using the application layer, the tag may be used as an EEPROM with read/write operation. It
is not necessary to know how STR710 communicates with the CRX14 coupler chip and how
CRX14 communicates with SR176 tag.
Figure 1.
Architecture details
RF - ASK Mod
STR710
CRX14
I2C
RF-BPSK mod
Tag
Firmware specifications
RFID firmware for STR710 supports SR176 tag
Firmware is developed on a 4 layer structure:
RFID reader/writer
Application layer: applications dedicated
functions
SR176 Commands
RF Commands layer: Initiate(), Select(),
Completion(), GetUID(), Read_Block(), Write_Block()
CRX14 Commands
Transceiver Commands layer: CRX14 registers
management
I2C Commands
7.1
I2C Bus layer: I2C protocol to interface CRX14
CRX14 demonstration kit
A demonstration kit has been created to interface CRX14 with the STR710 microcontroller
via I2C. Further details can be found in the application note AN1806. The demonstration kit
schematic and layout are shown below.
9/22
10/22
R2
E0
0R
R1
OP T
VCC
R4
E1
0R
R3
OP T
R6
E2
0R
R5
4
3
2
1
J1
CRX14
FL6
FL4
0R
0R
FL5 0R
WURT H 742-792-042 U 1
FL7
1
VCC
Vref
2
RF IN R F O U T
22nF50V
3
GND_RF
E0
4
OSC1
E1
5
OSC2
E2
6
GND
GND_RF
7
SCL
GND
8
GND
SDA
OP T C3
16
15
14
13
12
11
10
9
100nF50V
C6 VCC
SDA
+ C4
22uF 10V
VCC
C2
7pF50V
7pF50V
X1
13. 56MHz
C1
C8’
8pF50V
C7
120pF50V
C8
100pF50V
C7’
33pF50V
C5
10pF50V
R8
0R
R7
0R
ANT 2
ANT 1
Figure 2.
SCL
D1
1N4148 (OP T IONAL)
Overview of RFID reader using STR710
AN2399
CRX14 demonstration kit schematic
ai08488B
AN2399
Overview of RFID reader using STR710
Figure 3.
CRX14 demonstration kit layout
ai08489
ST has designed the CRX14, a short range contactless coupler chip, compliant with the
ISO14443 type B proximity standard. The CRX14 generates a 13.56 MHz signal. Designed
to deliver an RF power of 100 mW, it operates in the Short Range on contactless memory
tags (provided that they, too, are compliant with ISO14443 type B).
The CRX14 features the ST anti-collision mechanism, which allows the reader to detect and
identify all the tags that are present in the operating range, and to access them individually.
Because the CRX14 implements the France Telecom-proprietary anti-clone function, the
reader can also perform authentication of tags that are equipped with the France Telecom
anti-clone capability.
The CRX14 coupler interfaces between:
●
the memory tags, on one side, through input/output buffers and the ISO14443 type B
radio frequency protocol, and
●
the system master processor, on the other side, through a 400 kHz I2C bus.
Operating from a 5 V power supply, and delivered in a SO16N package, the CRX14 coupler
chip is an excellent solution for building contactless readers, embedded in the final
equipment, and offering a good compromise between operating range and cost.
11/22
Overview of RFID reader using STR710
7.2
AN2399
Interfacing with STR7xx using I2C peripheral
Due to the fact that the STR7xx microcontroller has a 3.3 voltage supply and the CRX14
device work at 5 V, a level shifter has to be inserted on the I2C bus in order to adjust the
voltage levels.
Figure 4.
Interfacing the I2C bus from 3.3 V to 5 V
The I2C Bus Interface on STR71x provides both multimaster and slave functions, and
controls all I2C bus-specific sequencing, protocol, arbitration and timing. It also supports fast
I2C mode (400 kHz).
For the purpose of this application note, the I2C peripheral works as Master
transmitter/receiver. In Master mode, it initiates a data transfer and generates the clock
signal. A serial data transfer always begins with a start condition and ends with a stop
condition. Both start and stop conditions are generated in master mode by hardware as
soon as the Master mode is selected.
Data and addresses are transferred as 8-bit bytes, MSB first. The first byte(s) following the
start condition contain the address (one in 7-bit mode, two in 10-bit mode).
A 9th clock pulse follows the 8 clock cycles of a byte transfer, during which the receiver must
send an acknowledge bit to the transmitter. Refer to Figure 5.
Figure 5.
I2C bus protocol
SDA
MSB
ACK
SCL
1
START
CONDITION
12/22
2
8
9
STOP
CONDITION
AN2399
Overview of RFID reader using STR710
Finally, I2C peripheral configuration has to be set as follows:
●
data width: 8-bit
●
Ack bit: enabled
●
Speed config: the user must configure it via I2C_frequency define in device_RFID.h file.
void init_CRX14_I2C(void){
u32 f_RFID=I2C_frequency;
/*------------------------------------------------------------------------------------------------------------------------Configure the SDA And the SCL pin of the I2C0 and I2C1 to alternate function Open
Drain
--------------------------------------------------------------------------------------------------------------------------*/
GPIO_Config (GPIO1,I2C0_SCL,GPIO_AF_OD);
GPIO_Config (GPIO1,I2C0_SDA,GPIO_AF_OD);
/*------------------------------------------------------------------------------------------------------------------------Configure I2C0 module
--------------------------------------------------------------------------------------------------------------------------*/
I2C_Init (I2C0);
I2C_FCLKConfig (I2C0);
I2C_OnOffConfig (I2C0, ENABLE);//Enable the I2C0
I2C_SpeedConfig (I2C0, f_RFID);//Configure the I2C0 speed
I2C_AddressConfig (I2C0,0xA2, I2C_Mode7);
//Configure the I2C0 address (to be used specially when this cell has to be adressed)
I2C_AcknowledgeConfig (I2C0, ENABLE);
//set str7 to send ack when receive data
}
13/22
RFID library
8
AN2399
RFID library
RFID library is developed using a 4-layer architecture. This section provides a brief
description of the layer functionality.
Figure 6.
RFID library: the 4 layer structure
RF - ASK Mod
STR710
I2C
CRX14
RF-BPSK mod
Tag
Firmware specifications
RFID firmware for STR710 supports SR176 tag
Firmware is developed on a 4 layer structure:
RFID reader/writer
Application layer: applications dedicated
functions
SR176 Commands
RF Commands layer: Initiate(), Select(),
Completion(), GetUID(), Read_Block(), Write_Block()
CRX14 Commands
Transceiver Commands layer: CRX14 registers
management
I2C Commands
8.1
I2C Bus layer: I2C protocol to interface CRX14
RFID reader/writer: the application layer
The RFID EEPROM memory may be accessed directly using the application layer. It allows
read/write operations on RFID EEPROM with different access options. Moreover, the
application layer implements the Finite State Machine (FSM) which allows each device to be
searched for and selected close to the antenna reader.
/*-----------------------------------------------------------------RFID Application Layer
-----------------------------------------------------------------Input:
- RFID_Action: 3 bit
bit 0: 1=ENABLE 64UID request, 0=DISABLE 64UID request
bit 1: 1=ENABLE READ request, 0=DISABLE READ request
bit 2: 1=ENABLE WRITE request, 0=DISABLE WRITE request
- TX_frame:
TX buffer pointer (write operations)
- TX_lenght:
TX buffer lenght (write operations)
- TX_offset:
TX offset for write operations
- RX_frame:
RX buffer pointer (read operations)
- RX_lenght:
RX buffer lenght (read operations)
- RX_offset:
RX offset for read operations
- RFID_UID:
64 bits RFID UID
- RFID_timeout: timeout for RFID polling (number of times STR7 is trying to search
tag)
Output:
- RX_frame:
RX buffer pointer (read operations)
- RFID_UID:
64 bits RFID UID
Return:
- Status:
14/22
AN2399
RFID library
bit0: 1-No tag selected; 0-tag selected
bit1: 1-Error on 64UID; 0-no error
bit2: 1-Error on READ; 0-no error
bit3: 1-Error on WRITE; 0-no error
bit4: 1-Error on Completion; 0-no error
bit5: 1-Error on RF_OFF; -no error
--------------------------------------------------------------------*/
RFID_status = RFID_Handler(RFID_Action,
&TX_frame[0],
TX_lenght,
TX_offset,
&RX_frame[0],
RX_lenght,
RX_offset,
&RFID_UID[0],
RFID_Polling_timeout);
8.1.1
RFID actions
Three main actions are available:
●
Read: RFID EEPROM
●
Write: RFID EEPROM
●
Get 64-bit UID (unique identifier)
The user can choose actions to perform on the device using the RFID_Action parameter: 3
bits allow each action to be chosen separately.
8.1.2
RFID memory access
Two different ways to access RFID EEPROM in read/write mode are available. The user can
choose to:
●
access (read/write) all 10 words (20 bytes) available on SR176 tag starting from base
address 0x0;
●
access (read/write) a portion of memory (one or more words) starting from an offset
address.
The following must be provided by the user:
8.1.3
●
a pointer related to the buffer he want to read/write;
●
the buffer length;
●
the offset where he want to start to read/write.
RFID polling
The user can choose how many times to search for a tag device close to the antenna reader
using the RFID_Polling_timeout parameter.
15/22
RFID library
8.1.4
AN2399
RFID communication status report
The communication status can be checked using the RFID_Handler return parameter. It
returns:
●
Presence/absence of tag into the space covered from magnetic field.
●
Error on reading/writing RFID EEPROM
●
Error getting 64 bits UID
●
Error on cut-off RF carrier.
In order to access an RFID EEPROM, the application layer function has to implement a
Finite State Machine (FSM) as depicted in the following picture:
Figure 7.
RFID: state transition diagram
POWER-OFF
Out of
Field
In Field
READY
INITIATE()
ACTIVE
Out of
Field
Out of
Field
SELECT(Chip_ID)
SELECTED
SELECT(Chip_ID)
COMPLETION
Out of
Field
DEACTIVATED
DESELECTED
SELECT(≠Chip_ID)
SELECT(Chip_ID)
READ_BLOCK()
WRITE_BLOCK()
PROTECT_BLOCK()
GET_PROTECTION()
When invoking the application layer, FSM searches for a tag (for a period of time specified in
RFID_Polling_timeout); when a tag device is found, the FSM attempts to recover the tag
CHIP_ID using the “Initiate()” command. If the tag responds with its own CHIP_ID the FSM
attempts to select it in order to perform actions according the RFID_Action parameter.
The FSM performs these actions using the “init_RFID()”. It describes all states from
POWER OFF to SELECTED.
When selected, the application layer FSM uses three functions to perform the requested
actions:
●
GetSR176_64UID(&RFID_UID[0]);
●
ReadSR176_EEPROM(&RX_frame[0],RX_offset,RX_lenght);
●
WriteSR176_EEPROM(&TX_frame[0],TX_offset,TX_lenght);
When all requested actions are performed, the FSM deselects the tag device via a
“Completion()” command.
16/22
AN2399
RFID library
Every time the RFID_Handler is invoked it powers the antenna with the 13.56 MHz carrier;
before exiting, it cuts-off the RF carrier.
8.2
SR176 commands layer
In order to manage the RFID tag, the CRX14 uses a set of commands. They are both used
to activate and select each device and to access (read/write or get 64 bits UID) the tag
EEPROM.
Here are all the functions used for reported RFID tags:
●
RF_ON();
// power on carrier frequency
●
RF_OFF();
// power off carrier frequency
●
Initiate(&RX_frame[0]);
// search a tag in the field
●
Select (RFID_CHIPID,&RX_frame[0]);// activate a tag in the field
●
Completion ( &RX_framebuf[0]);
// deselect tag
●
Time_Read();
// program time for read
●
ReadBlock (address, &RX_frame[ 0 ]);// read a word
●
Time_Write();
●
WriteBlock (address, &TX_frame[ 0 ], &RX_frame[0]); // write a word
// program time for write
Each RF command has a dedicated 16-bit code (see SR176 and CRX14 datasheet). Tags
in the field recognize it and perform the required operation (activation, read, write,
deactivation, etc.).
RF Commands functions use CRX14 commands to access CRX14 registers. Basically each
RF command performs a write operation and a read operation to a CRX14 register.
8.3
CRX14 commands layer
This layer provides all functions needed to interface the STR710 microcontroller with the
CRX14 coupler device. CRX14 device uses 6 control registers to communicate both with the
microcontroller (via I2C) and the tag (via RF circuitry).
Figure 8.
CRX14 control register access scheme
I2C
CONTROL REGISTER
RF CIRCUITRY
Depending on which register the user would like to access in read or write mode, several
functions are implemented.
17/22
RFID library
AN2399
Table 2.
Control registers
Address
00h
01h
02h
03h
8.3.1
Register
Length
Parameter Register
Access
Purpose
W
Set parameter register
R
Read parameter register
W
Store and send request frame to the
PICC. Wait for PICC answer frame
R
Transfer PICC answered frame data to
host
W
Start the Authentication process
R
Get the Authentication process
W
Launch the automated anti-collision
process from Slot_0 to Slot_15
R
Return data FFh
1 Byte
Input/Output Frame
Register
36 Bytes
Authenticate Register
NA
Slot Marker Register
1 Byte
04h
ST Reserved
NA
R and W
ST Reserved. Must not be used
05h
ST Reserved
NA
R and W
ST Reserved. Must not be used
CRX14 parameter register access
Figure 9.
CRX14 parameter register: write operation
S
T
A
R
T
Bus Master
CRX14 Write
R/W
Device Select
Code
Parameter Register
Address
1 0 1 0 X X X
00h
Register Byte
Value
S
T
O
P
data
Bus Slave
ACK
ACK
ACK
Figure 10. CRX14 parameter register: read operation
Bus Master
CRX14 Read
S
T
A
R
T
R/W
Device Select
Code
Parameter Register
Address
1 0 1 0 X X X
00h
R
E
S
T
A
R
T
R/W
Device Select
Code
1 0 1 0 X X X
data
Bus Slave
ACK
ACK
Here are the functions used for parameter register access:
int Write_CRX14_PR(UCHAR *DATA)
int Read_CRX14_PR(UCHAR *DATA)
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ACK
Register Byte
Value
S
T
O
P
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8.3.2
RFID library
CRX14 I/O frame register access
The Input/Output Frame Register is a 36-byte buffer that is accessed serially from Byte 0
through to Byte 35 (see Figure 11). It is located at the I²C address 01h. The Input/Output
Frame Register is the buffer in which the CRX14 stores the data Bytes of the request frame
to be sent to the PICC. It automatically stores the data Bytes of the answer frame received
from the PICC. The first Byte (Byte 0) of the Input/Output Frame Register is used to store
the frame length for both transmission and reception.
Figure 11. CRX14 I/O frame register description
Byte 0
Byte 1
Byte 2
Frame Length
1st data Byte
2nd data Byte
Byte 3
...
Byte 34
Byte 35
Last data Byte
<------------- Request and Answer Frame Bytes exchanged on the RF ------------->
00h No Byte transmitted
FFh CRC Error
xxh Number of transmitted Bytes
When accessed in I²C Write mode , the register stores the request frame Bytes that are to
be transmitted to the PICC. Byte 0 must be set with the request frame length (in Bytes) and
the frame is stored from Byte 1 onwards. At the end of the transmission, the 16-bit CRC is
automatically added. After the transmission, CRX14 waits for the PICC to send back an
answer frame. When correctly decoded, the PICC answer frame bytes are stored in the
Input/Output Frame Register from Byte 1 onwards. Byte 0 stores the number of bytes
received from the PICC.
Figure 12. CRX14 I/O frame register: write operation
Bus
Master
CRX14
Write
Bus
Slave
S
T
A
R
T
R/W
Device
Select
Code
Input/Output
Register
Address
1 0 1 0 XX X
PICC
Command
Code
Request Frame
Length N
01h
N
ACK
ACK
PICC
Command
Parameter
Data 1
ACK
PICC
Command
Parameter
Data 2
ACK
S
T
O
P
PICC
Command
Parameter
Data N
ACK
ACK
ACK
When accessed in I²C Read mode, the Input/Output Register sends back the last PICC
answer frame Bytes, if any, with Byte 0 transmitted first. The 16-bit CRC is not stored, and it
is not sent back on the I²C bus. The Input/Output Frame Register is set to all 00h between
transmission and reception. If there is no answer from the PICC, Byte 0 is set to 00h. In the
case of a CRC error, Byte 0 is set to FFh, and the data Bytes are discarded and not
appended in the register.
Figure 13. CRX14 I/O frame register: read operation
R/W
S
Input/Output
Device
T
Register
Select
Bus
A
Address
Code
Master R
T
CRX14
1 0 1 0XXX
01h
Read
Bus
Slave
ACK
R
E
S
T
A
R
T
ACK
R/W
ACK
ACK
ACK
NoACK
Device
Select
Code
1 0 1 0 XXX
ACK
S
T
O
P
N
Received
ACK Frame
Length
Data1
Answer
Frame
Data
Data N
Data 2
Answer
Frame
Data
Answer
Frame
Data
Answer
Frame
Data
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AN2399
Here are the functions used for I/O Frame register access:
int Write_CRX14_IOFR(UCHAR *DATA)
int Read_CRX14_IOFR(UCHAR *DATA)
8.4
I2C commands layer
The I2C layer provides all the functionalities to access and manage the I2C peripheral on
STR710. It is a part of the STR710 library. Some functionality was added in order to receive
a status when data is sent or received on the I2C bus; two programmable timeouts
(I2C_TIMEOUT_SEND and I2C_TIMEOUT_RECEIVE) inform the application layer about
any send/receive failure on I2C bus.
Below the code added for I2C_ByteSend and I2C_ByteReceive functions.
8.4.1
I2C_ByteSend_with_status function
/***************************************************************
* Function Name : I2C_ByteSend
* Description
: Send a single byte of data.
* Input
: I2Cx ( I2C0 or I2C1 )
*
Data : the byte to be sent to the slave
* Return
: status: 0-byte sent, 1-transmission error.
***************************************************************/
u8 I2C_ByteSend_with_status (I2C_TypeDef *I2Cx, u8 Data)
{
u8 status=0;
u32 timeout=I2C_TIMEOUT_SEND;
//Wait until the I2C_BTF bit is set
while (((I2Cx->SR1 & 0x08)==0)&&timeout--);
if(!timeout) status=1;
//Write in the DR register the byte to be sent
I2Cx->DR = Data;
return status;
}
8.4.2
I2C_ByteReceive_with_status function
/**********************************************************************
* Function Name : I2C_ByteReceive
* Description
: Returns the received byte.
* Input
: I2Cx ( I2C0 or I2C1 )
* Output
: Data ( variable where store read data )
* Return
: status: 0-byte sent, 1-transmission error.
***********************************************************************/
u8 I2C_ByteReceive_with_status (I2C_TypeDef *I2Cx, u8 *Data)
{
u8 status=0;
u32 timeout=I2C_TIMEOUT_RECEIVE;
//Wait till I2C_BTF bit is set
while (((I2Cx->SR1 & 0x08)==0)&&timeout--);
if(!timeout) status=1;
(*Data)=I2Cx->DR;
return status;
}
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9
Revision history
Revision history
Table 3.
Document revision history
Date
Revision
31-Jan-2008
1
Changes
Initial release.
21/22
AN2399
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