MCRF450 Просмотр технического описания (PDF) - Microchip Technology

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MCRF450

13.56 MHz Read/Write Passive RFID Device

Microchip Technology 

MCRF450/451/452/455

32-bit Tag ID and TC are included in the FR response.

An example for the calculation of the matching code is

given in Example 9-2.

EQUATION 6-2: BIT-WISE EQUATION FOR

“MATCH”

“Match” = Tag ID bit range a: b

{4*TC} modulo 32: {4 (TC +1) + 3} modulo 32

where {} modulo 32 means the remainder of {}

divided by 32. For example, {28} modulo 32 and {35}

modulo 32 are 28 and 3, respectively.

6.3 Time Slot Generator

This block generates time slots for the device. The time

slot represents the time delay between the end of the

FRR command and the beginning of the FR response.

The available time slots are 1, 16 or 64. One time slot

represents 2.5 ms. The device calculates the actual

time slot based on the TSMAX, TC and Tag ID. The

maximum time slot (TSMAX) is assigned to the device

by the FRR command (see Figures 6-3 to 6-7), or set

to 16, if the TF bit is set.

Four or six bits out of the 32-bit Tag ID are used to

calculate the time slot, with TC being the shift

parameter to choose which portion of the 32-bit Tag ID

is used, as shown in Equation 6-3.

EQUATION 6-3: TIME SLOT CALCULATION

TSMAX

Time Slot = Tag ID bit range a:b

64

{[4(TC+1)+1] modulo 32: [4 TC] modulo 32} XOR TC LSB

16

{[4(TC+1)-1] modulo 32: [4 TC] modulo 32} XOR TC LSB

1

0

Note:

The exclusive-or (XOR) operation in Equation 6-3 is called “semi-inverting” in that it randomizes worst case

tag IDs; for example: a Tag ID of ‘77777777’ or ‘00000000’. Table 6-10 shows examples of the

calculation.

TABLE 6-10: EXAMPLE: TAG ID = h´825FE1A0

Relevant Tag ID

TC

Hexadecimal

Binary

Selected Tag ID before

XOR with LSB of TC

TSMAX = 16 TSMAX = 64

Calculated Time Slot (TS)

(after XOR with LSB of TC)

TSMAX = 16

TSMAX = 64

0 h´825FE1(A0)´ b’1010 0000’

h´0´

1 h´825FE(1A)0´ b’0001 1010’

h´A´

2 h´825F(E1)A0´ b’1110 0001’

h´1´

3 h´825(FE)1A0´ b’1111 1110’

h´E´

4 h´82(5F)E1A0´ b’0101 1111’

h´F´

5 h´8(25)FE1A0´ b’0010 0101’

h´5´

6 h´(82)5FE1A0´ b’1000 0010’

h´2´

7 h´(08)25FE1A´ b’0000 1000’

h´8´

Legend: h´x..x´ represents hexadecimal number

d´x..x´ represents decimal number

b´x..x´ represents binary number

h´20´

h´1A´

h´21´

h´3E´

h´1F´

h´25´

h´02´

h´08´

h´0´

d´0´ h´20´ d´32´

h´5´

d´5´ h´25´ d´37´

h´1´

d´1´ h´21´ d´33´

h´1´

d´1´ h´01´ d´1´

h´F´ d´15´ h´1F´ d´31´

h´A´ d´10´ h´1A´ d´26´

h´2´

d´2´ h´02´ d´2´

h´7´

d´7´ h´37´ d´55´

Table 6-10 shows the calculated time slot (TS): 5 for

TC = 1 and TSMAX = 16 with Tag ID = h´825FE1A0´.

This means the device waits for 12.5 ms (5 x 2.5 ms =

12.5 ms) in a nonmodulating condition between the

end of FRR and the start of the FR response.

6.4 TIME SLOT COUNTER

This section generates the Sleep time (2.5 ms x TS) of

the device. During the Sleep time, the device remains

in a nonmodulating condition.

Also, the TS is 37 for TC = 1 and TSMAX = 64. This

means the device waits for 92.5 ms (37 x 2.5 ms =

92.5 ms) between the end of FRR and the start of the

FR response in a nonmodulating condition.

 2003 Microchip Technology Inc.

DS40232H-page 31

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