Serial Ports
12-29
Peripherals
Data is shifted to the left (LSB to MSB). Figure 12–20 illustrates what happens
when words less than 32 bits are shifted into the serial port. In this figure, it is
assumed that an 8-bit word is being received and that the upper three bytes
of the receive buffer are originally undefined. In the first portion of the figure,
byte
a has been shifted in. When byte b is shifted in, byte a is shifted to the left.
When the data-receive register is read, both bytes
a and b are read.
Figure 12–20. Receive Buffer Shift Operation
After byte a
After byte b
31
24
23
16
15
8
7
0
X
X
X
a
X
X
a
b
←
Shift direction
←
12.2.9 Serial-Port Operation Configurations
Several configurations are provided for the operation of the serial-port clocks
and timer. The clocks for each serial port can originate either internally or exter-
nally. Figure 12–21 shows serial-port clocking in the I/O mode (CLKXFUNC
= 0) when CLKX is either an input or an output. Figure 12–22 shows clocking
in the serial-port mode (CLKXFUNC=1). Both figures use a transmit section
for an example. The same relationship holds for a receive section.
