ST62T45B STMicroelectronics, ST62T45B Datasheet - Page 46

• Manufacturer Part Number: ST62T45B
• Description: 8-BIT OTP/EPROM MCU
• Manufacturer: STMicroelectronics

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45
ST62T45B/E45B
4.4 SERIAL PERIPHERAL INTERFACE (SPI)
The on-chip SPI is an optimized serial synchro-
nous interface that supports a wide range of in-
dustry standard SPI specifications. The on-chip
SPI is controlled by small and simple user soft-
ware to perform serial data exchange. The serial
shift clock can be implemented either by software
(using the bit-set and bit-reset instructions), with
the on-chip Timer 1 by externally connecting the
SPI clock pin to the timer pin or by directly apply-
ing an external clock to the Scl line.
The peripheral is composed by an 8-bit Data/shift
Register and a 4-bit binary counter while the Sin
pin is the serial shift input and Sout is the serial
shift output. These two lines can be tied together
to implement two wires protocols (I C-bus, etc).
When data is serialized, the MSB is the first bit.
Sin has to be programmed as input. For serial out-
Figure 25. SPI Block Diagram
46/72
Sout
SCL
Sin
I/O Port
I/O Port
I/O Port
1
0
OPR Reg.
Data Reg
Direction
Data Reg
Direction
Data Reg
Direction
DIN
CLK
DOUT
RESET
CP
CP
DIN
8-Bit Tristate Data I/O
put operation Sout has to be programmed as
open-drain output.
The SCL, Sin and Sout SPI clock and data signals
are connected to 3 I/O lines on the same external
pins. With these 3 lines, the SPI can operate in the
following operating modes: Software SPI, S-BUS,
I C-bus and as a standard serial I/O (clock, data,
enable). An interrupt request can be generated af-
ter eight clock pulses. Figure 25 shows the SPI
block diagram.
The SCL line clocks, on the falling edge, the shift
register and the counter. To allow SPI operation in
slave mode, the SCL pin must be programmed as
input and an external clock must be supplied to
this pin to drive the SPI peripheral.
In master mode, SCL is programmed as output, a
clock signal must be generated by software to set
and reset the port line.
(Q4=High after Clock8)
D0............... .............D7
to Processor Data Bus
SPI Interrupt Disable Register
Shift Register
4-Bit Counter
8-Bit Data
RESET
SPI Data Register
Enable
Output
DOUT
Reset
Load
Q4
Q4
Read
Write
Set Res
Interrupt
VR01504