MC68HC05E0 Datasheet, PDF (67/96 Pages) Motorola, Inc – High-density complementary metal oxide semiconductor (HCMOS) microcontroller unit

8
SERIAL INTERFACE
8.1
General
The serial interface (SI) on the MC68HC05E0 supports synchronous data transfer over one
bidirectional data line and a clock line. The interface can be configured to operate as a serial
peripheral interface (SPI) or as an I2C-bus interface. The microprocessor always has control of
the clock signal, and is therefore always “bus master”. The clock and data lines are multiplexed
through port E. Port E and the serial interface lines are controlled by two serial port select bits
(PS1, PS0) in the Port E/SI Mode Register ($0010.
8
Port E/SI mode register
Address bit 7
bit 6
bit 5
bit 4
bit 3
bit 2
bit 1
bit 0
State
on reset
$0010 SIE CPHA CPOL WL BD‘1 BD0 PS1 PS0 0000 0000
Table 8-1 PS0, PS1: Serial Port Function Selection Bits
PS1 PS0
0
0
0
1
1
0
1
1
Function
Port Eas parallel port
I²C bus protocol
SPI function
SPI function
PE0 PE1 PE2
I/O
I/O
I/O
data clock I/O
data clock I/O
data I/O clock
Note that bit 3 of port E is always available as a port bit.
When PS0 and PS1 are set to select a serial function, the data register and direction register bits
for the pins used as data and clock do not influence the state of these pins.
MC68HC05E0
SERIAL INTERFACE
MOTOROLA
8-1