HT46R068B/HT46R069B
Enhanced A/D Type 8-bit OTP MCU
Serial Interface Module – SIM
These devices contain a Serial Interface Module, which includes both the four line SPI interface
or the two line I2C 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 I2C based hardware such as sensors,
Flash or EEPROM memory, etc. The SIM interface pins are pin-shared with other I/O 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 I2C 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
This SPI interface function which is part of the Serial Interface Module, should not be confused
with the other independent SPI function, known as SPIA, which is described in another section of
this datasheet.
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
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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 I2C 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. Communi-
cation 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.
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SPI Master/Slave Connection
Rev. 1.00
80
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HOLTEK [ HOLTEK SEMICONDUCTOR INC ]
