Microchip Technology AC244049 Data Sheet
PIC16(L)F1825/1829
DS41440C-page 314
2010-2012 Microchip Technology Inc.
26.4
EUSART Synchronous Mode
Synchronous serial communications are typically used
in systems with a single master and one or more
slaves. The master device contains the necessary
circuitry for baud rate generation and supplies the clock
for all devices in the system. Slave devices can take
advantage of the master clock by eliminating the
internal clock generation circuitry.
There are two signal lines in Synchronous mode: a
bidirectional data line and a clock line. Slaves use the
external clock supplied by the master to shift the serial
data into and out of their respective receive and
transmit shift registers. Since the data line is
bidirectional, synchronous operation is half-duplex
only. Half-duplex refers to the fact that master and
slave devices can receive and transmit data but not
both simultaneously. The EUSART can operate as
either a master or slave device.
Start and Stop bits are not used in synchronous
transmissions.
in systems with a single master and one or more
slaves. The master device contains the necessary
circuitry for baud rate generation and supplies the clock
for all devices in the system. Slave devices can take
advantage of the master clock by eliminating the
internal clock generation circuitry.
There are two signal lines in Synchronous mode: a
bidirectional data line and a clock line. Slaves use the
external clock supplied by the master to shift the serial
data into and out of their respective receive and
transmit shift registers. Since the data line is
bidirectional, synchronous operation is half-duplex
only. Half-duplex refers to the fact that master and
slave devices can receive and transmit data but not
both simultaneously. The EUSART can operate as
either a master or slave device.
Start and Stop bits are not used in synchronous
transmissions.
26.4.1
SYNCHRONOUS MASTER MODE
The following bits are used to configure the EUSART
for Synchronous Master operation:
• SYNC = 1
• CSRC = 1
• SREN = 0 (for transmit); SREN = 1 (for receive)
• CREN = 0 (for transmit); CREN = 1 (for receive)
• SPEN = 1
Setting the SYNC bit of the TXSTA register configures
the device for synchronous operation. Setting the CSRC
bit of the TXSTA register configures the device as a
master. Clearing the SREN and CREN bits of the RCSTA
register ensures that the device is in the Transmit mode,
otherwise the device will be configured to receive. Setting
the SPEN bit of the RCSTA register enables the
EUSART.
for Synchronous Master operation:
• SYNC = 1
• CSRC = 1
• SREN = 0 (for transmit); SREN = 1 (for receive)
• CREN = 0 (for transmit); CREN = 1 (for receive)
• SPEN = 1
Setting the SYNC bit of the TXSTA register configures
the device for synchronous operation. Setting the CSRC
bit of the TXSTA register configures the device as a
master. Clearing the SREN and CREN bits of the RCSTA
register ensures that the device is in the Transmit mode,
otherwise the device will be configured to receive. Setting
the SPEN bit of the RCSTA register enables the
EUSART.
26.4.1.1
Master Clock
Synchronous data transfers use a separate clock line,
which is synchronous with the data. A device configured
as a master transmits the clock on the TX/CK line. The
TX/CK pin output driver is automatically enabled when
the EUSART is configured for synchronous transmit or
receive operation. Serial data bits change on the lead-
ing edge to ensure they are valid at the trailing edge of
each clock. One clock cycle is generated for each data
bit. Only as many clock cycles are generated as there
are data bits.
which is synchronous with the data. A device configured
as a master transmits the clock on the TX/CK line. The
TX/CK pin output driver is automatically enabled when
the EUSART is configured for synchronous transmit or
receive operation. Serial data bits change on the lead-
ing edge to ensure they are valid at the trailing edge of
each clock. One clock cycle is generated for each data
bit. Only as many clock cycles are generated as there
are data bits.
26.4.1.2
Clock Polarity
A clock polarity option is provided for Microwire
compatibility. Clock polarity is selected with the SCKP
bit of the BAUDCON register. Setting the SCKP bit sets
the clock Idle state as high. When the SCKP bit is set,
the data changes on the falling edge of each clock.
compatibility. Clock polarity is selected with the SCKP
bit of the BAUDCON register. Setting the SCKP bit sets
the clock Idle state as high. When the SCKP bit is set,
the data changes on the falling edge of each clock.
Clearing the SCKP bit sets the Idle state as low. When
the SCKP bit is cleared, the data changes on the rising
edge of each clock.
the SCKP bit is cleared, the data changes on the rising
edge of each clock.
26.4.1.3
Synchronous Master Transmission
Data is transferred out of the device on the RX/DT pin.
The RX/DT and TX/CK pin output drivers are automat-
ically enabled when the EUSART is configured for
synchronous master transmit operation.
A transmission is initiated by writing a character to the
TXREG register. If the TSR still contains all or part of a
previous character the new character data is held in the
TXREG until the last bit of the previous character has
been transmitted. If this is the first character, or the
previous character has been completely flushed from
the TSR, the data in the TXREG is immediately
transferred to the TSR. The transmission of the
character commences immediately following the
transfer of the data to the TSR from the TXREG.
Each data bit changes on the leading edge of the
master clock and remains valid until the subsequent
leading clock edge.
The RX/DT and TX/CK pin output drivers are automat-
ically enabled when the EUSART is configured for
synchronous master transmit operation.
A transmission is initiated by writing a character to the
TXREG register. If the TSR still contains all or part of a
previous character the new character data is held in the
TXREG until the last bit of the previous character has
been transmitted. If this is the first character, or the
previous character has been completely flushed from
the TSR, the data in the TXREG is immediately
transferred to the TSR. The transmission of the
character commences immediately following the
transfer of the data to the TSR from the TXREG.
Each data bit changes on the leading edge of the
master clock and remains valid until the subsequent
leading clock edge.
26.4.1.4
Synchronous Master Transmission
Setup:
Setup:
1.
Initialize the SPBRGH, SPBRGL register pair
and the BRGH and BRG16 bits to achieve the
desired baud rate (see
and the BRGH and BRG16 bits to achieve the
desired baud rate (see
2.
Enable the synchronous master serial port by
setting bits SYNC, SPEN and CSRC.
setting bits SYNC, SPEN and CSRC.
3.
Disable Receive mode by clearing bits SREN
and CREN.
and CREN.
4.
Enable Transmit mode by setting the TXEN bit.
5.
If 9-bit transmission is desired, set the TX9 bit.
6.
If interrupts are desired, set the TXIE bit of the
PIE1 register and the GIE and PEIE bits of the
INTCON register.
PIE1 register and the GIE and PEIE bits of the
INTCON register.
7.
If 9-bit transmission is selected, the ninth bit
should be loaded in the TX9D bit.
should be loaded in the TX9D bit.
8.
Start transmission by loading data to the
TXREG register.
TXREG register.
Note:
The TSR register is not mapped in data
memory, so it is not available to the user.
memory, so it is not available to the user.