PIC16LF18854 Datasheet, PDF (469/668 Pages) Microchip Technology – C Compiler Optimized RISC Architecture

PIC16(L)F18856/76
31.2.6 SPI OPERATION IN SLEEP MODE
In SPI Master mode, module clocks may be operating
at a different speed than when in Full-Power mode; in
the case of the Sleep mode, all clocks are halted.
Special care must be taken by the user when the MSSP
clock is much faster than the system clock.
In Slave mode, when MSSP interrupts are enabled,
after the master completes sending data, an MSSP
interrupt will wake the controller from Sleep.
If an exit from Sleep mode is not desired, MSSP
interrupts should be disabled.
In SPI Master mode, when the Sleep mode is selected,
all module clocks are halted and the transmis-
sion/reception will remain in that state until the device
wakes. After the device returns to Run mode, the
module will resume transmitting and receiving data.
In SPI Slave mode, the SPI Transmit/Receive Shift
register operates asynchronously to the device. This
allows the device to be placed in Sleep mode and data
to be shifted into the SPI Transmit/Receive Shift
register. When all eight bits have been received, the
MSSP interrupt flag bit will be set and if enabled, will
wake the device.
31.3 I²C MODE OVERVIEW
The Inter-Integrated Circuit (I²C) bus is a multi-master
serial data communication bus. Devices communicate
in a master/slave environment where the master
devices initiate the communication. A slave device is
controlled through addressing.
The I²C bus specifies two signal connections:
• Serial Clock (SCL)
• Serial Data (SDA)
Figure 31-11 shows the block diagram of the MSSP
module when operating in I²C mode.
Both the SCL and SDA connections are bidirectional
open-drain lines, each requiring pull-up resistors for the
supply voltage. Pulling the line to ground is considered
a logical zero and letting the line float is considered a
logical one.
Figure 31-11 shows a typical connection between two
processors configured as master and slave devices.
The I²C bus can operate with one or more master
devices and one or more slave devices.
There are four potential modes of operation for a given
device:
• Master Transmit mode
(master is transmitting data to a slave)
• Master Receive mode
(master is receiving data from a slave)
• Slave Transmit mode
(slave is transmitting data to a master)
• Slave Receive mode
(slave is receiving data from the master)
To begin communication, a master device starts out in
Master Transmit mode. The master device sends out a
Start bit followed by the address byte of the slave it
intends to communicate with. This is followed by a
single Read/Write bit, which determines whether the
master intends to transmit to or receive data from the
slave device.
If the requested slave exists on the bus, it will respond
with an Acknowledge bit, otherwise known as an ACK.
The master then continues in either Transmit mode or
Receive mode and the slave continues in the comple-
ment, either in Receive mode or Transmit mode,
respectively.
A Start bit is indicated by a high-to-low transition of the
SDA line while the SCL line is held high. Address and
data bytes are sent out, Most Significant bit (MSb) first.
The Read/Write bit is sent out as a logical one when the
master intends to read data from the slave, and is sent
out as a logical zero when it intends to write data to the
slave.
FIGURE 31-11:
I²C MASTER/
SLAVE CONNECTION
VDD
SCL
VDD
Master
SDA
SCL
Slave
SDA
The Acknowledge bit (ACK) is an active-low signal,
which holds the SDA line low to indicate to the transmit-
ter that the slave device has received the transmitted
data and is ready to receive more.
The transition of a data bit is always performed while
the SCL line is held low. Transitions that occur while the
SCL line is held high are used to indicate Start and Stop
bits.
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Preliminary
DS40001824A-page 469