ST92196A STMicroelectronics, ST92196A Datasheet - Page 189

• Manufacturer Part Number: ST92196A
• Description: 8/16-bit Mcu For Tv Applications With Up To 96k Rom, On-screen-display And 1 Or 2 Data Slicers
• Manufacturer: STMicroelectronics

SERIAL PERIPHERAL INTERFACE (Cont’d)
8.10.8 IM-bus Interface
The IM-bus features a bidirectional data line and a
clock line; in addition, it requires an IDENT line to
distinguish an address byte from a data byte
ure
protocol sends the least significant bit first; this re-
quires a software routine which reverses the bit or-
der before sending, and after receiving, a data
byte.
an IM-bus peripheral and an ST9 SPI. The SDO
and SDI pins are connected to the bidirectional
data pin of the peripheral device. The SDO alter-
nate function is configured as Open-Drain (exter-
nal 2.5K
With this type of configuration, data is sent to the
peripheral by writing the data byte to the SPIDR
register. To receive data from the peripheral, the
user should write FFh to the SPIDR register, in or-
der to generate the shift clock pulses. As the SDO
Figure 79. ST9 and IM-bus Peripheral
n
Figure 80. IM bus Timing
189/268
- SERIAL PERIPHERAL INTERFACE (SPI)
CLOCK LINE
DATA LINE
PROTOCOL
80). Unlike the I
ST9 MCU
IM-BUS
Figure 79
IDENT
PORTX
SDO
SCK
pull-up resistors are required).
SDI
shows the connections between
LSB
2
C-bus protocol, the IM-bus
1
2
2x
2.5 K
V
3
DD
CLOCK
DATA
IDENT
4
DEVICE
IM-BUS
SLAVE
VR001427
5
6
(Fig-
MSB
line is set to the Open-Drain configuration, the in-
coming data bits that are set to “1” do not affect the
SDO/SDI line status (which defaults to a high level
due to the FFh value in the transmit register), while
incoming bits that are set to “0” pull the input line
low.
In software it is necessary to initialise the ST9 SPI
by setting both CPOL and CPHA to “1”. By using a
general purpose I/O as the IDENT line, and forcing
it to a logical “0” when writing to the SPIDR regis-
ter, an address is sent (or read). Then, by setting
this bit to “1” and writing to SPIDR, data is sent to
the peripheral. When all the address and data
pairs are sent, it is necessary to drive the IDENT
line low and high to create a short pulse. This will
generate the stop condition.
LSB
1
2
3
4
5
6
MSB
VR000172