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XC161 Derivatives
Peripheral Units (Vol. 2 of 2)
High-Speed Synchronous Serial Interface (SSC)
User’s Manual
19-9
V2.2, 2004-01
SSC_X, V2.0
Figure 19-4
SSC Full-Duplex Configuration
The data output pins MRST of all slave devices are connected together onto the one
receive line in the configuration shown in
. During a transfer, each slave
shifts out data from its shift register. There are two ways to avoid collisions on the receive
line due to different slave data:
•
Only one slave drives the line, i.e. enables the driver of its MRST pin. All the other
slaves must have their MRST pins programmed as input so only one slave can put
its data onto the master’s receive line. Only receiving data from the master is
possible. The master selects the slave device from which it expects data either by
separate select lines, or by sending a special command to this slave. The selected
slave then switches its MRST line to output until it gets a de-selection signal or
command.
In the configuration depicted in
, Device #2 is the slave which has its
output driver enabled as push/pull output. Device #3 is an inactive slave, it needs to
disable its output driver by programming the pin to input mode.
•
The slaves use their MRST outputs in open-drain mode. This forms a wired-AND
connection. The receive line needs an external pull-up in this case. Corruption of the
Clock
MCA05457
Master
Device #1
Transmit
Receive
Clock
MTSR
SCLK
MRST
Shift Register
Clock
MTSR
SCLK
MRST
Shift Register
Clock
Device #2
Slave
MTSR
SCLK
MRST
Shift Register
Device #3
Slave
Symbols
Input
Push/Pull Output
Open-Drain Output
Tri-Stated = Input