參數(shù)資料
型號: 16LF628A
廠商: Microchip Technology Inc.
元件分類: 8位微控制器
英文描述: FLASH-Based 8-Bit CMOS Microcontrollers
中文描述: 基于閃存的8位CMOS微控制器
文件頁數(shù): 81/168頁
文件大?。?/td> 3760K
代理商: 16LF628A
2002 Microchip Technology Inc.
Preliminary
DS40044A-page 79
PIC16F627A/628A/648A
12.2.2
USART ASYNCHRONOUS
RECEIVER
The receiver block diagram is shown in Figure 12-8.
The data is received on the RB1/RX/DT pin and drives
the data recovery block. The data recovery block is
actually a high-speed shifter operating at x16 times the
baud rate, whereas the main receive serial shifter oper-
ates at the bit rate or at F
OSC
.
When Asynchronous mode is selected, reception is
enabled by setting bit CREN (RCSTA<4>).
The heart of the receiver is the receive (serial) shift reg-
ister (RSR). After sampling the STOP bit, the received
data in the RSR is transferred to the RCREG register (if
it is empty). If the transfer is complete, flag bit RCIF
(PIR1<5>) is set. The actual interrupt can be enabled/
disabled
by
setting/clearing
(PIE1<5>). Flag bit RCIF is a read-only bit, which is
cleared by the hardware. It is cleared when the RCREG
register has been read and is empty. The RCREG is a
enable
bit
RCIE
double buffered register, (i.e., it is a two deep FIFO). It
is possible for two bytes of data to be received and
transferred to the RCREG FIFO and a third byte begin
shifting to the RSR register. On the detection of the
STOP bit of the third byte, if the RCREG register is still
full then overrun error bit OERR (RCSTA<1>) will be
set. The word in the RSR will be lost. The RCREG reg-
ister can be read twice to retrieve the two bytes in the
FIFO. Overrun bit OERR has to be cleared in software.
This is done by resetting the receive logic (CREN is
cleared and then set). If bit OERR is set, transfers from
the RSR register to the RCREG register are inhibited,
so it is essential to clear error bit OERR if it is set. Fram-
ing error bit FERR (RCSTA<2>) is set if a STOP bit is
detected as clear. Bit FERR and the 9th receive bit are
buffered the same way as the receive data. Reading
the RCREG, will load bits RX9D and FERR with new
values, therefore it is essential for the user to read the
RCSTA register before reading RCREG register in
order not to lose the old FERR and RX9D information.
FIGURE 12-8:
USART RECEIVE BLOCK DIAGRAM
x64 Baud Rate CLK
SPBRG
Baud Rate Generator
RB1/RX/DT
Pin Buffer
and Control
SPEN
Data
Recovery
CREN
OERR
FERR
RSR register
MSb
LSb
RX9D
RCREG register
FIFO
Interrupt
RCIF
RCIE
Data Bus
8
3 64
or
3 16
Stop
Start
(8)
7
1
0
RX9
2 2 2
RX9
ADEN
RX9
ADEN
RSR<8>
Enable
Load of
Receive
Buffer
8
8
RCREG register
RX9D
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