PIC16F627A Datasheet, PDF (77/168 Pages) Microchip Technology – FLASH-Based 8-Bit CMOS Microcontrollers

PIC16F627A/628A/648A
The data on the RB1/RX/DT pin is sampled three times
by a majority detect circuit to determine if a high or a
low level is present at the RX pin. If bit BRGH
(TXSTA<2>) is clear (i.e., at the low baud rates), the
sampling is done on the seventh, eighth and ninth fall-
ing edges of a x16 clock (Figure 12-3). If bit BRGH is
set (i.e., at the high baud rates), the sampling is done
on the 3 clock edges preceding the second rising edge
after the first falling edge of a x4 clock (Figure 12-4 and
Figure 12-5).
FIGURE 12-1:
RX PIN SAMPLING SCHEME. BRGH = 0
RX
(RB1/RX/DT pin)
Baud CLK
START bit
bit0
Baud CLK for all but START bit
x16 CLK
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 1 2 3
Samples
FIGURE 12-2:
RX PIN SAMPLING SCHEME, BRGH = 1
RX pin
START Bit
bit0
bit1
Baud CLK
x4 CLK
Q2, Q4 CLK
First falling edge after RX pin goes low
Second rising edge
1 2 34 12 3 4 1 2
Samples
Samples
Samples
FIGURE 12-3:
RX PIN SAMPLING SCHEME, BRGH = 1
RX pin
START Bit
bit0
Baud CLK
x4 CLK
Q2, Q4 CLK
Baud CLK for all but START bit
First falling edge after RX pin goes low
Second rising edge
1
2
3
4
Samples
 2002 Microchip Technology Inc.
Preliminary
DS40044A-page 75