MCRF450 데이터 시트보기 (PDF) - Microchip Technology

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MCRF450

13.56 MHz Read/Write Passive RFID Device

Microchip Technology 

MCRF450/451/452/455

6.0 READ/WRITE ANTI-COLLISION

LOGIC

This section includes the anti-collision algorithm of the

device and consists of the Anti-collision/command

controller, the time slot generator and the time slot

counter.

6.1 Description of Algorithm

The read/write anti-collision algorithm is based on time

division multiplexing of tag responses. Each device is

allowed to communicate with the Interrogator in its time

slot only. When not in its assigned time slot, the device

remains in a nonmodulating condition. This enables the

Interrogator to communicate with other devices in the

same Interrogator field with fewer chances of data

collision.

Figure 6-1 shows the anti-collision algorithm flowchart,

which consists of four control loops. They are:

Detection, Processing, Sleeping and Reactivation

loops. All devices in the Interrogator’s RF field are

controlled by five different commands and internal

control flags.

The Interrogator commands are:

1. Fast Read Request (FRR): If the TF bit (bit 30

or Block 0) is cleared, the device responds only

to the FRR command. The FRR command

consists of five specially timed gap pulses (refer

to Figures 6-3 to 6-7). The position of the five

gap pulses in the given time span (1.575 ms)

determines the parameters of the command.

The command has three parameters: TCMAX,

TSMAX and Data transmission speed. The

details of these parameters will be discussed in

the following sections. If the device receives the

FRR command, it sends the FR response

and then listens for 1 ms (TLW) for a matching

code from the Interrogator.

2. Fast Read Bypass (FRB): This command is

used in the Reactivation loop and is only appli-

cable to a device with the FR bit (bit 31 in Block

0) cleared. The device responds with 64 bits of

data, which includes Block 1 data (32-bit Tag

ID), and then listens for 1 ms (TLW) for a match-

ing code from the Interrogator. The command

structure is the same as the FRR command: five

specially timed gap pulses (1.575 ms). The

command parameter (Figure 6-8) determines

the data rate (normal speed or fast speed) of

subsequent Interrogator commands.

3. Matching Code 1 (MC1): This command

consists of time calibration pulses (TCP)

followed by 1-of-16 PPM signals. It is used when

the device does not need any further process-

ing. This MC1 command causes a device, which

is in the detection loop, to enter the sleeping

loop.

4. Matching Code 2 (MC2): The command

structure is the same as MC1: TCP followed by

1-of-16 PPM signals. The command is used

when the device needs further processing (read/

write). The device enters the processing loop if

it receives this command in the detection loop.

The MC1 and MC2 matching code command

consists of 12 bits or 3 symbols. The first 8 bits,

or the first two symbols, are selected from the

32-bit Tag ID. The next 4 bits, or the 3rd symbol,

determine the matching code type (3 bits) and a

parity bit (see Section 6.2.3.6 “Calculation Of

Matching Code”). The command lasts for

about 11.2 ms, including the TCP.

5. End Process (EP): This command consists of

the time reference pulses followed by

1-of-16 PPM signals. The EP command causes

a device to exit the processing loop and enter

the sleeping loop.

6.1.1 DETECTION LOOP

If the FR bit (bit 31 of Block 0) is set, the device can

enter this loop in two ways, depending on the condition

of the TF bit (bit 30 of Block 0). They are:

1. When the TF bit is cleared, the device enters

this loop and waits for a FRR command. This is

called the “Interrogator-Talks-First” (ITF) mode.

2. When the TF bit is set, the device enters this

loop by transmitting the FR response without

waiting for an FRR command. This is called the

“Tag-Talks-First” (TTF) mode.

For case 1 above, the parameters of the FRR are:

• Maximum number of time slots

(TSMAX = 1, 16, or 64),

• Maximum transmission counter

(TCMAX = 1, 2, or 4),

• Data transmission speed (Normal or Fast mode).

The purpose of the TSMAX and TCMAX parameters is

to acknowledge the device in the detection loop as fast

as possible. TSMAX represents the maximum number

of time slots between the end of the FRR command and

the beginning of the FR response. One time slot

(TSLOT) represents 2.5 ms. For example, TSMAX = 64

represents a maximum time delay of 160 ms before

sending the FR response. See Section 6.3 “Time

Slot Generator” for the calculation of actual time

delay. TCMAX represents the maximum number of FR

responses a device can send after an FRR command.

For example, TCMAX = 4 means the device can send

its FR response four times (after the FRR command)

for acknowledgment (matching code).

DS40232H-page 16

 2003 Microchip Technology Inc.

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