Microchip Technology AC244045 Data Sheet
2010-2012 Microchip Technology Inc.
DS41440C-page 313
PIC16(L)F1825/1829
26.3.4
BREAK CHARACTER SEQUENCE
The EUSART module has the capability of sending the
special Break character sequences that are required by
the LIN bus standard. A Break character consists of a
Start bit, followed by 12 ‘0’ bits and a Stop bit.
To send a Break character, set the SENDB and TXEN
bits of the TXSTA register. The Break character
transmission is then initiated by a write to the TXREG.
The value of data written to TXREG will be ignored and
all ‘0’s will be transmitted.
The SENDB bit is automatically reset by hardware after
the corresponding Stop bit is sent. This allows the user
to preload the transmit FIFO with the next transmit byte
following the Break character (typically, the Sync
character in the LIN specification).
The TRMT bit of the TXSTA register indicates when the
transmit operation is active or Idle, just as it does during
normal transmission. See
special Break character sequences that are required by
the LIN bus standard. A Break character consists of a
Start bit, followed by 12 ‘0’ bits and a Stop bit.
To send a Break character, set the SENDB and TXEN
bits of the TXSTA register. The Break character
transmission is then initiated by a write to the TXREG.
The value of data written to TXREG will be ignored and
all ‘0’s will be transmitted.
The SENDB bit is automatically reset by hardware after
the corresponding Stop bit is sent. This allows the user
to preload the transmit FIFO with the next transmit byte
following the Break character (typically, the Sync
character in the LIN specification).
The TRMT bit of the TXSTA register indicates when the
transmit operation is active or Idle, just as it does during
normal transmission. See
for the timing of
the Break character sequence.
26.3.4.1
Break and Sync Transmit Sequence
The following sequence will start a message frame
header made up of a Break, followed by an auto-baud
Sync byte. This sequence is typical of a LIN bus
master.
1.
header made up of a Break, followed by an auto-baud
Sync byte. This sequence is typical of a LIN bus
master.
1.
Configure the EUSART for the desired mode.
2.
Set the TXEN and SENDB bits to enable the
Break sequence.
Break sequence.
3.
Load the TXREG with a dummy character to
initiate transmission (the value is ignored).
initiate transmission (the value is ignored).
4.
Write ‘55h’ to TXREG to load the Sync character
into the transmit FIFO buffer.
into the transmit FIFO buffer.
5.
After the Break has been sent, the SENDB bit is
reset by hardware and the Sync character is
then transmitted.
reset by hardware and the Sync character is
then transmitted.
When the TXREG becomes empty, as indicated by the
TXIF, the next data byte can be written to TXREG.
TXIF, the next data byte can be written to TXREG.
26.3.5
RECEIVING A BREAK CHARACTER
The Enhanced EUSART module can receive a Break
character in two ways.
The first method to detect a Break character uses the
FERR bit of the RCSTA register and the Received data
as indicated by RCREG. The Baud Rate Generator is
assumed to have been initialized to the expected baud
rate.
A Break character has been received when;
• RCIF bit is set
• FERR bit is set
• RCREG = 00h
The second method uses the Auto-Wake-up feature
described in
character in two ways.
The first method to detect a Break character uses the
FERR bit of the RCSTA register and the Received data
as indicated by RCREG. The Baud Rate Generator is
assumed to have been initialized to the expected baud
rate.
A Break character has been received when;
• RCIF bit is set
• FERR bit is set
• RCREG = 00h
The second method uses the Auto-Wake-up feature
described in
. By enabling this feature, the EUSART will
sample the next two transitions on RX/DT, cause an
RCIF interrupt, and receive the next data byte followed
by another interrupt.
Note that following a Break character, the user will
typically want to enable the Auto-Baud Detect feature.
For both methods, the user can set the ABDEN bit of
the BAUDCON register before placing the EUSART in
Sleep mode.
RCIF interrupt, and receive the next data byte followed
by another interrupt.
Note that following a Break character, the user will
typically want to enable the Auto-Baud Detect feature.
For both methods, the user can set the ABDEN bit of
the BAUDCON register before placing the EUSART in
Sleep mode.
FIGURE 26-9:
SEND BREAK CHARACTER SEQUENCE
Write to TXREG
Dummy Write
BRG Output
(Shift Clock)
Start bit
bit 0
bit 1
bit 11
Stop bit
Break
TXIF bit
(Transmit
Interrupt Flag)
TX (pin)
TRMT bit
(Transmit Shift
Empty Flag)
SENDB
(send Break
control bit)
SENDB Sampled Here
Auto Cleared