Holtek BC45B4523, Руководство пользователя, Страница: 62 / 96

Rev. 1.20 62 October 28, 2020
BC45B4523
Low Frequency Oscillator
Low Frequency
Oscillator
( LFO )
CLK 16.38kHz
LFO
Tuning
ManLFOTrimValue
LFOTrimResult
CLK 13.56MHz
ManLFOTrim
LFO_Code
LFOTune
Command
Low Frequency Oscillator and Tuning Block Diagram
The device contains tuneable low frequency oscillator, which generates clock 16.38kHz for wake up card detection
system. The above figure shows the block diagram of oscillator system. Output clock frequency is tuneable by
8-bit LFO_Code signals, which is determined by ManLFOTrim bit (Sector1-0x03.0). If ManLFOTrim is set
to 1, the value of ManLFOTrimValue (Sector1-0x02) is passed to LFO_Code. While clearing this bit to 0, the
LFOTrimResult (Sector1-0x01) from automatic tuning system will be applied for tuning.
The LFO Tuning circuit trims output clock to desired frequency by comparing to the standard clock 13.56MHz.
The tuning mechanism is start when LFOTune command is executed, or after the device is power up.
FIFO Buffer
The device contains a 64-byte FIFO for buffering input and output data stream between the external
microcontroller and the internal codec. In normal transmission and reception to/from air, transmitted data should
be written into the FIFO before executing. In contrast, reading received data from FIFO can be performed
immediately after a single byte of data becomes available. Functions of registers associated with the FIFO are
listed as below.
Register Address.Bit Indication Set By Clear By
FIFOData Sector0-0x02
Input end and Output end of buffer for
external microcontroller
— —
FIFOLength Sector0-0x04
Number of bytes already stored in the
FIFO-buffer (distance between write-and
read-pointer)
Write data to FIFO
Read data from FIFO Set FlushFIFO
HiAlert Sector0-0x03.1
Flag to indicate amount of data in FIFO ≥
(64 - WaterLevel)
FIFO ≥
(64 -WaterLevel)
FIFO <
(64 - WaterLevel)
LoAlert Sector0-0x03.0
Flag to indicate amount of data in FIFO ≤
WaterLevel
FIFO ≤ WaterLevel FIFO > WaterLevel
HiAlertIEn Sector0-0x06.1 HiAlert interrupt enable External Controller External Controller
LoAlertIEn Sector0-0x06.0 LoAlert interrupt enable External Controller External Controller
HiAlertIRq Sector0-0x07.1 HiAlert interrupt flag
HiAlert changes
from 0 to 1
External Controller
LoAlertIRq Sector0-0x07.0 LoAlert interrupt flag
LoAlert changes
from 0 to 1
External Controller
FIFOOvf Sector0-0x0A.4 Flag to indicate FIFO was written while
FIFO is already full
Write FIFO while
FIFOLength=64
Set FlushFIFO
FlushFIFO Sector0-0x09.0 Clear FIFO. FIFOLength becomes to zero External Controller —
WaterLevel Sector0-0x29
Define the level of FIFO for overflow and
underflow warning
External Controller —
Registers Associated with FIFO