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HT66F0175/HT66F0185
A/D Flash MCU with EEPROM
HT66F0175/HT66F0185
A/D Flash MCU with EEPROM
Serial Interface Module – SIM
These devices contain a Serial Interface Module, which includes both the four-line SPI interface or
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 other I/O pins and therefore the
SIM interface functional pins must first be selected using the corresponding pin-shared function
selection bits. 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 pins are selected using pull-
high control registers when the SIM function is enabled and the corresponding pins are used as SIM
input pins.
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 devices can be
either master or slave. Although the SPI interface specification can control multiple slave devices
from a single master, these devices 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 pins must first
be selected by configuring the pin-shared function selection bits and setting the correct bits in the
SIMC0 and SIMC2 registers. After the desired SPI configuration has been set it can be 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 devices only contain
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.
The SPI function in these devices offer 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 devices
are in the master or slave mode and upon the condition of certain control bits such as CSEN and
SIMEN.
