UCBRSx
7 m
[i]
UCBRFx
j 0
m
[ j]
+
=
å
t
[i] =
bit,RX
1
f
BRCLK
(
(
(16 × UCBRx) +
15
j = 0
m
[j] + m
[i]
UCBRFx
UCBRSx
t
[i] = t
+
bit,RX
SYNC
(8 *
UCBRx) +
T
[j] +
bit,RX
i – 1
j = 0
1
f
BRCLK
(
(
m
[j]
UCBRFx
7
j = 0
+ m
[i]
UCBRSx
T
[j] +
bit,RX
i – 1
j = 0
1
f
BRCLK
t
[i] = t
+
bit,RX
SYNC
INT(½UCBRx) + m
[i]
UCBRSx
(
(
1 2 3
4 5 6
0
i
t
0
t
ideal
7 8
1
2
9 10 11 12 13 14 1 2 3
4 5 6 7 8
9 10 11 12 13 14 1 2 3
4 5 6 7
ST
D0
D1
D0
D1
ST
Synchronization Error ± 0.5x BRCLK
Majority Vote Taken
Majority Vote Taken
Majority Vote Taken
BRCLK
UCAxRXD
RXD synch.
t
actual
Sample
RXD synch.
t
0
t
1
t
1
t
2
eUSCI_A Operation – UART Mode
781
SLAU367P – October 2012 – Revised April 2020
Copyright © 2012–2020, Texas Instruments Incorporated
Enhanced Universal Serial Communication Interface (eUSCI) – UART Mode
Figure 30-11. Receive Error
The ideal sampling time t
bit,ideal,RX
[i] is in the middle of a bit period:
t
bit,ideal,RX
[i] = (1/baud rate)(i + 0.5)
The real sampling time, t
bit,RX
[i], is equal to the sum of all previous bits according to the formulas shown in
the transmit timing section, plus one-half BITCLK for the current bit i, plus the synchronization error t
SYNC
.
This results in the following t
bit,RX
[i] for the low-frequency baud-rate mode:
Where:
T
bit,RX
[i] = (1/f
BRCLK
)(UCBRx + m
UCBRSx
[i])
m
UCBRSx
[i] = Modulation of bit i of UCBRSx
For the oversampling baud-rate mode, the sampling time t
bit,RX
[i] of bit i is calculated by:
Where:
= Sum of ones from columns 0 to (7 + m
UCBRSx
[i]) from the corresponding row in
m
UCBRSx
[i] = Modulation of bit i of UCBRSx
This results in an error normalized to one ideal bit time (1/baud rate) according to the following formula:
Error
RX
[i] = (t
bit,RX
[i] – t
bit,ideal,RX
[i]) × baud rate × 100%
30.3.13 Typical Baud Rates and Errors
Standard baud-rate data for UCBRx, UCBRSx, and UCBRFx are listed in
for a 32768-Hz
crystal sourcing ACLK and typical SMCLK frequencies. Make sure that the selected BRCLK frequency
does not exceed the device specific maximum eUSCI_A input frequency (see the device-specific data
sheet).