Serial Interface Module
-
SIM
These devices contain a Serial Interface Module, which includes both the four line SPI interface or the
two line I
2
C interface types, to allow an easy method of communication with external peripheral
hardware. Having relatively simple communication protocols, these serial interface types allow the
microcontroller to interface to external SPI or I
2
C based hardware such as sensors, Flash or EEPROM
memory, etc. The SIM pins are pin shared with other I/O pins and must be selected using the SIMEN
bit in the SIMC0 register. As both interface types share the same pins and registers, the choice of
whether the SPI or I
2
C type is used is made using the SIM operating mode control bits, named
SIM2~SIM0, in the SIMC0 register.
SPI Interface
The SPI interface is often used to communicate with external peripheral devices such as sensors, Flash
or EEPROM memory devices etc. Originally developed by Motorola, the four line SPI interface is a
synchronous serial data interface that has a relatively simple communication protocol simplifying the
programming requirements when communicating with external hardware devices.
The communication is full duplex and operates as a slave/master type, where the device can be either
master or slave. Although the SPI interface specification can control multiple slave devices from a
single master, but this device provided only one SCS pin. If the master needs to control multiple slave
devices from a single master, the master can use I/O pin to select the slave devices.
SPI Interface Operation
The SPI interface is a full duplex synchronous serial data link. It is a four line interface with pin names
SDI, SDO, SCK and SCS. Pins SDI and SDO are the Serial Data Input and Serial Data Output lines,
SCK is the Serial Clock line and SCS is the Slave Select line. As the SPI interface pins are pin-shared
with normal I/O pins and with the I
2
C function pins, the SPI interface must first be enabled by setting
the correct bits in the SIMC0 and SIMC2 registers. Communication between devices connected to the
SPI interface is carried out in a slave/master mode with all data transfer initiations being implemented
by the master. The Master also controls the clock signal. As the device only contains a single SCS pin
only one slave device can be utilized. The SCS pin is controlled by software, set CSEN bit to
²
1
²
to
enable SCS pin function, set CSEN bit to
²
0
²
the SCS pin will be as I/O function.
The SPI function in this device offers the following features:
·
Full duplex synchronous data transfer
·
Both Master and Slave modes
·
LSB first or MSB first data transmission modes
·
Transmission complete flag
·
Rising or falling active clock edge
The status of the SPI interface pins is determined by a number of factors such as whether the device
is in the master or slave mode and upon the condition of certain control bits such as CSEN and
SIMEN.
BS83B08-3/B12-3/B16-3/B16G-3/C24-3
8-Bit Touch Key Flash MCU
Rev. 1.50
81
April 28, 2020
S P I M a s t e r
S P I S l a v e
S C K
S D O
S D I
S C S
S C K
S D I
S D O
S C S
SPI Master/Slave Connection
