M93C86, M93C76, M93C66, M93C56, M93C46
Connecting to the serial bus
2
Connecting to the serial bus
shows an example of three memory devices connected to an MCU, on a serial 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-down resistor R (represented in
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 may be in a state where all inputs/outputs are 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 low): this ensures that C does not become high at the same time as S goes low, and
so, that the t
SLCH
requirement is met. The typical value of R is 100 kΩ.
Figure 3.
Bus master and memory devices on the serial bus
V
SS
V
CC
R
SDO
SDI
SCK
Bus master
C Q D
V
CC
V
SS
R
CS3 CS2 CS1
S
ORG
S
ORG
S
ORG
M93xxx
memory device
R
M93xxx
memory device
C Q D
V
CC
V
SS
R
M93xxx
memory device
C Q D
V
CC
V
SS
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STMICROELECTRONICS [ STMICROELECTRONICS ]
