Microchip Technology SAM Series User Manual

CAUTION
The user must discard the first received byte in the case where the UART clocks were disabled in
Low-Power mode and transitioned to Active mode as a result of remote Tx start bit detection.
Figure 11-8. UART RS232 Design Example Diagram
UART RS232 PROTECTION EXAMPLE
MCU
UxRX
UxTX
DB9
↑Transient Suppressors
1
3
2
CDSOT23-T24CAN
5
9
4
8
3
7
2
6
1
NOTE:
The TVS ground MUST be tied directly to ground
plane not to a ground trace to minimize inductance.
In addition, TVS should be located as close to the
external DB9 connector as possible
MI0805J102R-10
RS232Conn
Opt(B)
Chassis
(AC) Gnd
if available
(Preferred)
If chassis (AC) Gnd
not available
Opt(A)
10K
SHEILD
MAX3221
SP2
32E
CN-
2
7
4
3
6
5
15
3.3v
V+
V-
VCC
C1+
C1-
C2-
C2+
ROUT
DIN
DOUT
RIN
0.1uf
0.1uf
14
GND
0.1µf
0.1µf
13
11
8
9
0.1uf
EN/
FORCEON
12
1
FORCEOFF/
3.3v
16
3.3v
10k
10k
10
NOTE:
See appropriate MCU power
bypassing circuit configuration
illustrations in section 2.2
1k ohms @ 100Mhz DC=0.15Ω, 1A
NOTE:
MI0805J102R-10
11.5.1 Key UART Protection Design Points
• On the RS232 DB9 connector shown in the figure above, the “SHIELD” is NOT directly tied to the digital signal
ground which is a typical design error
. Not connecting the SHIELD to the digital ground ensures that an ESD
discharge event does not infiltrate the digital ground system and disrupt normal application operation, which
results in an MCU reset or component failure. Attach the shield to the chassis ground. If the chassis ground is
not accessible, then connect through either:
– 1k Ohms @ 100 MHz Ferrite Bead 1A, DCR = 0.15 Ohm for ESD protection only concerns.
– Recommended: A 10k fixed resistor adds the same ESD protection as the ferrite bead but with the
additional benefit of ground loop current isolation between the remote system shield or case and the local
digital ground in the event that the remote system did not follow good design practices. 10K is still low
enough to shunt and attenuate the RF and EMI on the RS232 cable shield.
• The UART has the RS232 DB9 digital ground connector, pin 5, the ferrite bead, and the 10 Ohm resistor. The
ferrite bead protects against a possible ESD ground discharge event from the remote system, and the 10 Ohm
resistor is to limit potential ground loop currents (see Ground Loops), while not effecting signal VIL/VIH and
VOL/VOH levels.
• Transient voltage suppressors on the UART signal lines entering and leaving the local system complete the
protection
Serial Data Corruption Errors
© 2022 Microchip T
echnology Inc.
and its subsidiaries
Manual
DS70005439B-page 42

Microchip Technology SAM Series Specifications

General

Brand	Microchip Technology
Model	SAM Series
Category	Microcontrollers
Language	English