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

The TSMAX and TCMAX values are determined by the

Interrogator’s decision on how many tags are in the

field. The Interrogator may assign TSMAX = 1 and

TCMAX = 1, assuming there is only one tag in the field.

The efficiency of the detection will increase in multiple

tag environments by assigning a higher number to both

the TSMAX and TCMAX. If the device receives the

FRR, it clears the Position 1 flag, waits for its time slot,

replies with the FR response and then listens for 1 ms.

The FR response consists of a maximum of 160

Manchester data bits (default: 96 bits), which includes

the 32-bit Tag ID and the FRF data (Blocks 3-5) (see

Table 6-3 and Example 9-1).

To acknowledge the FR response, the Interrogator can

start to send a matching code (MC) during the device’s

1 ms listening window (TLW). The MC is encoded with

1-of-16 PPM signal (see Figure 6-9). The MC1 is given

to the device if the device does not need any further

processing. If the device receives the MC1, it enters the

sleeping loop and stays in the loop in a nonmodulating

condition. The MC2 command is given to the device if

further processing (read/write) is required. If the device

receives the MC2 command, it enters the processing

loop.

If the device misses the MC within the listening window,

it sends the FR response again after its time slot when

two conditions are met: (1) Position 1 flag is cleared

and, (2) TCMAX has not elapsed. The device checks

the condition (elapsed or not elapsed) of TCMAX using

an internal transmission counter (TC). The TC consists

of 3 bits. If the Position 1 flag is cleared, the device

increments the TC by 1 each time it does not receive a

MC during its listening window. See Figure 6-1 for a

flow chart showing the conditional incrementing of the

transmission counter. Table 6-1 shows an example of

detecting the elapsed TCMAX using a rolling modulo-8

transmission counter.

For the TTF case, the device repeats its FR response

(as long as it is energized) according to the TCMAX

and TSMAX parameters, as specified in Table 7-5.

Even though the device is operating in the TTF mode,

it will respond to its correct MC during its listening

window. If TCMAX = 1, 2 or 4, it will also respond to

FRR commands, just as in the ITF case (see

Section 6.1.1.1 “Matching Code Queuing”).

6.1.1.1 Matching Code Queuing

Once the device receives the FRR command, it sends

the FR response and waits for a matching code (MC)

during its listening window. If the device does not

receive its correct MC code before its TCMAX has

elapsed (see Table 6-1), it goes back to the beginning

of the detection loop (position 1 in the loop) and waits

for either a new FRR command or for the MC1 or MC2

matching code. This is called “matching code queuing”.

In this queuing, the device stays in the detection loop

waiting for an Interrogator command (FRR or MC). This

queuing takes place within the detection loop and is

controlled by the conditions of "Set Position 1 Flag" and

TCMAX.

This queuing allows the Interrogator to communicate

with a device outside its listening window. The result is

enhanced and accelerated processing of individual

devices in a multiple tag environment.

TABLE 6-1:

CONDITIONS FOR

TCMAX = ELAPSED FOR ITF

MODE

Rolling

Modulo -8 TC

TCMAX

=1

TCMAX TCMAX

=2

=4

0 0 1 elapsed

—

—

0 1 0 elapsed elapsed

—

0 1 1 elapsed

—

—

1 0 0 elapsed elapsed elapsed

1 0 1 elapsed

—

—

1 1 0 elapsed elapsed

—

1 1 1 elapsed

—

elapsed

0 0 0 elapsed elapsed

—

6.1.2 PROCESSING LOOP

The reading and writing processes take place in this

loop. Devices in this loop are waiting for commands for

processing. In order to read from, or write to, the

device, its “Processing Flag” (PF) must be set. Any

device entering this loop with its PF cleared is called a

“follow-along” tag. This follow-along tag in the loop is

not processed for reading or writing.

If the device with the PF flag set receives the EP

command, it exits this loop and enters the sleeping

loop. However, the same EP command sends the

follow-along tag back to the detection loop.

If the device receives the FRR or FRB command in this

loop, it sees the command as invalid, resets itself and

goes back to the initial power-up state.

6.1.3 SLEEPING LOOP

The sleeping loop is used to keep all processed

devices in a “silent” condition. The devices stay in this

loop in a nonmodulating condition as long as they

remain in the field.

 2003 Microchip Technology Inc.

DS40232H-page 17

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