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M0A21/M0A23 Series
May 06, 2022
Page
444
of 746
Rev 1.02
M0
A21
/M
0
A
2
3
SE
RIES
TEC
H
NICAL
RE
FEREN
C
E
M
ANUAL
Active
nRTS pin output status of RS-485 function mode
(default)
Driver Enable
Set UART_MODEM[1]=0 by software
Set UART_MODEM[1]=1 by software
RTS control bit
(UART_MODEM[1])
RTSSTS
(UART_MODEM[13])
nRTS pin output
RTSACTLV = 0
RTSACTLV = 1
Note:
RS485AUD (UART_ALTCTL[10]) = 0, support nRTS control bit by software control only.
Figure 6.11-25 RS-485 nRTS Driving Level with Software Control
Programming Sequence Example:
1. Program FUNCSEL in UART_FUNCSEL to select RS-485 function.
2. Program the RXOFF (UART_FIFO[8]) to determine enable or disable the receiver RS-485
receiver.
3. Program the RS485NMM (UART_ALTCTL[8]) or RS485AAD (UART_ALTCTL[9]) mode.
4. If the RS485AAD (UART_ALTCTL[9]) mode is selected, the ADDRMV
(UART_ALTCTL[31:24]) is programmed for auto address match value.
5. Determine auto direction control by programming RS485AUD (UART_ALTCTL[10]).
Start
bit
D0
TX pin output
Driver Enable
RX
TX
nRTS
Differential Bus
RS- 485 Transceiver
UART / RS- 485 Controller
D1
D2
D3
D4
D5
D6
D7
P
Stop
bit
Driver Enable
RTSSTS
(UART_MODEM[13])
Note:
RS485AUD (UART_ALTCTL[10]) must be set to 1, and RTSACTLV (UART_MODEM[9]) must be set to 0.
Figure 6.11-26 Structure of RS-485 Frame