MFRC522 datasheet(49/109 Pages) NXP

49 / 109 page

112132

Product data sheet

Rev. 3.2 — 22 May 2007

49 of 109

NXP Semiconductors

MFRC522

Contactless Reader IC

10.3.2 Selection of the transfer speeds

The internal UART interface is compatible to an RS232 serial interface.

Table 140 “Selectable transfer speeds” describes examples for different transfer speeds

and relevant register settings.

The resulting transfer speed error is less than 1.5% for all described transfer speeds.

The default transfer speed is 9.6 kbit/s.

To change the transfer speed, the host controller has to write a value for the new transfer

speed to the register SerialSpeedReg. The bits BR_T0 and BR_T1 define factors to set

the transfer speed in the SerialSpeedReg.

Table 139 “Settings of BR_T0 and BR_T1” describes the settings of BR_T0 and BR_T1.

The selectable transfer speeds as shown in Table 140 “Selectable transfer speeds” are

calculated according to the following formulas:

if BR_T0=0: transfer speed = 27.12 MHz/(BR_T1+1)

if BR_T0>0: transfer speed = 27.12 MHz/(BR_T1 +33)/2^(BR_T0 -1)

Remark: Transfer speeds above 1228.8 k are not supported.

Table 139: Settings of BR_T0 and BR_T1

BR_T0

01234567

factor BR_T0

11248

range BR_T1

1 to 32

33 to 64

Table 140: Selectable transfer speeds

Transfer Speed [bit/s]

SerialSpeedReg

Transfer Speed Accuracy

decimal

heximal

7.2 k

250

FAh

-0.25%

9.6 k

235

EBh

0.32%

14.4 k

218

DAh

-0.25%

19.2 k

203

CBh

0.32%

38.4 k

171

ABh

0.32%

57.6 k

154

9Ah

-0.25%

115.2 k

122

7Ah

-0.25%

128 k

116

74h

-0.06%

230.4 k

5Ah

-0.25%

460.8 k

3Ah

-0.25%

921.6 k

1Ch

1.45%

1228.8 k

15h

0.32%

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