Rev. 1.40
88
March 29, 2019
Rev. 1.40
89
March 29, 2019
HT45F23A/HT45F24A
TinyPower
TM
Flash MCU with OPA & Comparators
HT45F23A/HT45F24A
TinyPower
TM
Flash MCU with OPA & Comparators
Serial Interface Module – SIM
The devices contain a Serial Interface Module respectively, 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 interface pins are pin-shared with PB0~PB3
pins therefore the SIM interface function must first be selected using a configuration option. 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. These
pull-high resistors of the SIM pin-shared I/O are selected using pull-high control registers, and also
if the SIM function is enabled.
SPI Interface
The SPI interface is often used to communicate with external peripheral device such as sensors,
Flash or EEPROM memory device 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 device.
The communication is full duplex and operates as a slave/master type, where the devices can be
either master or slave. Although the SPI interface specification can control multiple slave device
from a single master, but this device provides 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 PB0~PB3 pins and with the I
2
C function pins, the SPI interface must first be enabled by
selecting the SIM enable configuration option and setting the correct bits in the SIMC0 and SIMC2
registers. After the SPI configuration option has been configured it can also be additionally disabled
or enabled using the SIMEN bit in the SIMC0 register. 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 “1” to enable SCS pin function, set CSEN bit to “0” the SCS
pin will be floating state.
SPI Master/Slave Connection