sclt3-8bt8-tr STMicroelectronics, sclt3-8bt8-tr Datasheet - Page 12

• Manufacturer Part Number: sclt3-8bt8-tr
• Description: Protected Digital Input Termination With Serialized State Transfer
• Manufacturer: STMicroelectronics

Functional description
2.6.3
12/33
SPI transfer speed
The speed of the SPI is defined by the clock frequency and the data frame transfer time. In
the SCLT application the transfer time correspond to the input scanning time programmed
by the I/O controller.
In a 16-bit mode this scanning time should be less than 500 µs for a 64-input module (128
bits to transfer) where it should be about 160 µs for a 16-input module (32 bits to transfer).
To obtain such scanning with the data frame structure, the clock frequency is set
respectively at 256 kHz and 200 kHz.
Figure 9.
The clock frequency is limited by the application requirements to secure the immunity of the
SPI section against fast transient disturbances and keep the isolator consumption low
enough.
The SCLT maximum SPI clock frequency is 2 MHz.
●
●
In between two transfer sequences the output driver of the SPI circuit should go in high
impedance before any new transfer operation so falling edge of the chip select /CS:
t
DIS
MOSI
MISO
SCK
/CS
< t
The minimum SPI clock period is also defined by the capability of the SCLT to capture
data on MOSI and to write out data on MISO as shown in
–
–
At the start of the transfer sequence the first rising edge of the clock SCK should occur
after the data writing on the SPI output MISO corresponding with the propagation time
t
A
, avoiding missing the first data: t
DT
Capture rule: t
Write out rule: t
.
T
A
SCLT slave unit operation, input MOSI and output MISO timing diagrams
T
LD
MSB
MSB
M
S
CH
D
T
1
CH
+ t
> t
S
H
T
Doc ID 15191 Rev 3
D
< t
T
CL
T
CL
S
= t
T
14
14
2
H
C
LD
- t
> t
CH
A
+ t
S
15
1
1
T
FO
T
T
F
Table
RO
T
LSB
LSB
R
16
M
S
9.
T
HC
MSB
MSB
SCLT3-8BT8
M
S
T
DT