PIC18F97J60 Datasheet, PDF (321/474 Pages) Microchip Technology – 64/80/100-Pin, High-Performance, 1 Mbit Flash Microcontrollers with Ethernet

PIC18F97J60 FAMILY
20.3 EUSARTx Synchronous
Master Mode
The Synchronous Master mode is entered by setting
the CSRC bit (TXSTAx<7>). In this mode, the data is
transmitted in a half-duplex manner (i.e., transmission
and reception do not occur at the same time). When
transmitting data, the reception is inhibited and vice
versa. Synchronous mode is entered by setting bit
SYNC (TXSTAx<4>). In addition, enable bit, SPEN
(RCSTAx<7>), is set in order to configure the TXx and
RXx pins to CKx (clock) and DTx (data) lines,
respectively.
Clock polarity (CKx) is selected with the TXCKP bit
(BAUDCON<4>). Setting TXCKP sets the Idle state on
CKx as high, while clearing the bit sets the Idle state as
low. Data polarity (DTx) is selected with the RXDTP bit
(BAUDCONx<5>). Setting RXDTP sets the Idle state
on DTx as high, while clearing the bit sets the Idle state
as low. DTx is sampled when CKx returns to its Idle
state. This option is provided to support Microwire
devices with this module.
20.3.1 EUSARTx SYNCHRONOUS
MASTER TRANSMISSION
The EUSARTx transmitter block diagram is shown in
Figure 20-3. The heart of the transmitter is the Transmit
(Serial) Shift Register (TSR). The Shift register obtains
its data from the Read/Write Transmit Buffer register,
TXREGx. The TXREGx register is loaded with data in
software. The TSR register is not loaded until the last
bit has been transmitted from the previous load. As
soon as the last bit is transmitted, the TSR is loaded
with new data from the TXREGx (if available).
Once the TXREGx register transfers the data to the
TSR register (occurs in one TCY), the TXREGx is empty
and the TXxIF flag bit is set. The interrupt can be
enabled or disabled by setting or clearing the interrupt
enable bit, TXxIE. TXxIF is set regardless of the state
of enable bit TXxIE; it cannot be cleared in software. It
will reset only when new data is loaded into the
TXREGx register.
While flag bit TXxIF indicates the status of the TXREGx
register, another bit, TRMT (TXSTAx<1>), shows the
status of the TSR register. TRMT is a read-only bit which
is set when the TSR is empty. No interrupt logic is tied to
this bit, so the user must poll this bit in order to determine
if the TSR register is empty. The TSR is not mapped in
data memory so it is not available to the user.
To set up a Synchronous Master Transmission:
1. Initialize the SPBRGHx:SPBRGx registers for the
appropriate baud rate. Set or clear the BRG16
bit, as required, to achieve the desired baud rate.
2. Enable the synchronous master serial port by
setting bits SYNC, SPEN and CSRC.
3. If the signal from the CKx pin is to be inverted,
set the TXCKP bit. If the signal from the DTx pin
is to be inverted, set the RXDTP bit.
4. If interrupts are desired, set enable bit TXxIE.
5. If 9-bit transmission is desired, set bit TX9.
6. Enable the transmission by setting bit TXEN.
7. If 9-bit transmission is selected, the ninth bit
should be loaded in bit TX9D.
8. Start transmission by loading data to the
TXREGx register.
9. If using interrupts, ensure that the GIE and PEIE
bits in the INTCON register (INTCON<7:6>) are
set.
FIGURE 20-11: SYNCHRONOUS TRANSMISSION
Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4
Q3 Q4 Q1 Q2 Q3 Q4 Q1Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4
RC7/RX1/DT1
bit 0
bit 1
bit 2
bit 7
bit 0
bit 1
bit 7
RC6/TX1/CK1 pin
(TXCKP = 0)
Word 1
Word 2
RC6/TX1/CK1 pin
(TXCKP = 1)
Write to
TXREG1 Reg
TX1IF bit
(Interrupt Flag)
Write Word 1
Write Word 2
TRMT bit
TXEN bit
‘1’
‘1’
Note: Sync Master mode, SPBRG1 = 0, continuous transmission of two 8-bit words. This example is equally applicable to EUSART2
(RG1/TX2/CK2 and RG2/RX2/DT2).
© 2006 Microchip Technology Inc.
Advance Information
DS39762A-page 319