M95512-DR Ver la hoja de datos (PDF) - STMicroelectronics
Número de pieza
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M95512-DR Datasheet PDF : 48 Pages
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Connecting to the SPI bus
3
Connecting to the SPI bus
M95512-W, M95512-R
These devices are fully compatible with the SPI protocol.
All instructions, addresses and input data bytes are shifted in to the device, most significant
bit first. The Serial Data Input (D) is sampled on the first rising edge of the Serial Clock (C)
after Chip Select (S) goes low.
All output data bytes are shifted out of the device, most significant bit first. The Serial Data
Output (Q) is latched on the first falling edge of the Serial Clock (C) after the instruction
(such as the Read from Memory Array and Read Status Register instructions) have been
clocked into the device.
Figure 4. Bus master and memory devices on the SPI bus
R
SPI Interface with
(CPOL, CPHA) =
(0, 0) or (1, 1)
SDO
SDI
SCK
SPI Bus Master
VSS
VCC
CQD
VCC
VSS
CQD
VCC
VSS
C Q D VCC
VSS
CS3 CS2 CS1
R
SPI Memory R
Device
S
W HOLD
SPI Memory R
Device
SPI Memory
Device
S
W HOLD
S
W HOLD
AI12836b
1. The Write Protect (W) and Hold (HOLD) signals should be driven, high or low as appropriate.
Figure 4 shows an example of three memory devices connected to an MCU, on an SPI bus.
Only one device is selected at a time, so only one device drives the Serial Data Output (Q)
line at a time, the other devices are high impedance.
The pull-up resistor R (represented in Figure 4) ensures that no device is selected if the Bus
Master leaves the S line in the high impedance state.
In applications where the Bus Master might enter a state where all inputs/outputs SPI lines
are in high impedance at the same time (for example, if the Bus Master is reset during the
transmission of an instruction), the clock line (C) must be connected to an external pull-
down resistor so that, if all inputs/outputs become high impedance, the C line is pulled low
(while the S line is pulled high). This ensures that S and C do not become high at the same
time, and so, that the tSHCH requirement is met.
The typical value of R is 100 k,.
10/48
Doc ID 11124 Rev 13
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