
PIC16C7X
DS30390E-page 104
1997 Microchip Technology Inc.
12.1.1
SAMPLING
The data on the RC7/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-
set (i.e., at the high baud rates), the sampling is done
on the 3 clock edges preceding the second rising edge
FIGURE 12-3: RX PIN SAMPLING SCHEME. BRGH = 0 (PIC16C73/73A/74/74A)
FIGURE 12-4: RX PIN SAMPLING SCHEME, BRGH = 1 (PIC16C73/73A/74/74A)
FIGURE 12-5: RX PIN SAMPLING SCHEME, BRGH = 1 (PIC16C73/73A/74/74A)
RX
baud CLK
x16 CLK
Start bit
Bit0
Samples
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
1
2
3
Baud CLK for all but start bit
(RC7/RX/DT pin)
RX pin
baud clk
x4 clk
Q2, Q4 clk
Start Bit
bit0
bit1
First falling edge after RX pin goes low
Second rising edge
Samples
1
2
3
4
1
2341
2
RX pin
baud clk
x4 clk
Q2, Q4 clk
Start Bit
bit0
First falling edge after RX pin goes low
Second rising edge
Samples
12
3
4
Baud clk for all but start bit