HT95R45 Datasheet, PDF (30/76 Pages) Holtek Semiconductor Inc – Phone 8-Bit MCU with DTMF Receiver & CPT

HT95R45
The SIMDR register is used to store the data being
transmitted and received. The same register is used by
both the SPI and I²C functions. Before the
microcontroller writes data to the SPI bus, the actual
data to be transmitted must be placed in the SIMDR reg-
ister. After the data is received from the SPI bus, the
microcontroller can read it from the SIMDRregister. Any
transmission or reception of data from the SPI bus must
be made via the SIMDR register.
Bit 7 6 5 4 3 2 1 0
Label SD7 SD6 SD5 SD4 SD3 SD2 SD1 SD0
R/W R/W R/W R/W R/W R/W R/W R/W R/W
POR X X X X X X X X
There are also two control registers for the SPI inter-
face, SIMCTL0 and SIMCTL2. Note that the SIMCTL2
register also has the name SIMAR which is used by the
I²C function. The SIMCTL1 register is not used by the
SPI function, only by the I²C function. Register
SIMCTL0 is used to control the enable/disable function
and to set the data transmission clock frequency. Al-
though not connected with the SPI function, the
SIMCTL0 register is also used to control the Peripheral
Clock prescaler. Register SIMCTL2 is used for other
control functions such as LSB/MSB selection, write colli-
sion flag etc.
The following gives further explanation of each
SIMCTL1 register bit:
· SIMIDLE
The SIMIDLE bit is used to select if the SPI interface
continues running when the device is in the IDLE
mode. Setting the bit high allows the SPI interface to
maintain operation when the device is in the Idle
mode. Clearing the bit to zero disables any SPI opera-
tions when in the Idle mode.
This SPI/I²C idle mode control bit is located at
CLKMOD register bit4.
· SIMEN
The bit is the overall on/off control for the SPI inter-
face. When the SIMEN bit is cleared to zero to disable
the SPI interface, the SDI, SDO, SCK and SCS lines
will be in a floating condition and the SPI operating
current will be reduced to a minimum value. When the
bit is high the SPI interface is enabled. The SIMconfig-
uration option must have first enabled the SIM inter-
face for this bit to be effective. Note that when the
SIMEN bit changes from low to high the contents of
the SPI control registers will be in an unknown condi-
tion and should therefore be first initialised by the ap-
plication program.
· _SIM0~SIM2
These bits setup the overall operating mode of the SIM
function. As well as selecting if the I²C or SPI function,
they are used to control the SPI Master/Slave selec-
tion and the SPI Master clock frequency. The SPI
clock is a function of the system clock but can also be
chosen to be sourced from the Timer/Event Counter. If
the SPI Slave Mode is selected then the clock will be
supplied by an external Master device.
SIM0 SIM1 SIM2
SPI Master/Slave Clock
Control and I2C Enable
0
0
0 SPI Master, f_SYS/4
0
0
1 SPI Master, f_SYS/16
0
1
0 SPI Master, f_SYS/64
0
1
1 SPI Master, f_SUB
1
0
0
SPI Master Timer/Event
Counter 0 output/2
1
0
1 SPI Slave
1
1
0 I²C mode
1
1
1 Not used
SPI Control Register - SIMCTL2
The SIMCTL2 register is also used by the I²C interface
but has the name SIMAR.
· TRF
The TRF bit is the Transmit/Receive Complete flag and
is set high automatically when an SPI data transmis-
sion is completed, but must be cleared by the applica-
tion program. It can be used to generate an interrupt.
· _WCOL
The WCOL bit is used to detect if a data collision has
occurred. If this bit is high it means that data has been
attempted to be written to the SIMDR register during a
data transfer operation. This writing operation will be
ignored if data is being transferred. The bit can be
cleared by the application program. Note that using
the WCOL bit can be disabled or enabled via configu-
ration option.
· _CSEN
The CSEN bit is used as an on/off control for the SCS
pin. If this bit is low then the SCS pin will be disabled
and placed into a floating condition. If the bit is high
the SCS pin will be enabled and used as a select pin.
Note that using the CSEN bit can be disabled or en-
abled via configuration option.
· _MLS
This is the data shift select bit and is used to select
how the data is transferred, either MSB or LSB first.
Setting the bit high will select MSB first and low for
LSB first.
· _CKEG and _CKPOL
These two bits are used to setup the way that the
clock signal outputs and inputs data on the SPI bus.
These two bits must be configured before data trans-
fer is executed otherwise an erroneous clock edge
may be generated. The CKPOL bit determines the
base condition of the clock line, if the bit is high then
the SCK line will be low when the clock is inactive.
When the CKPOL bit is low then the SCK line will be
high when the clock is inactive. The CKEG bit deter-
mines active clock edge type which depends upon the
condition of CKPOL.
Rev. 1.00
30
March 12, 2010