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TC1796
Peripheral Units (Vol. 2 of 2)
Synchronous Serial Interface (SSC)
User’s Manual
20-7
V2.0, 2007-07
SSC, V2.1
When initializing the devices in this configuration, one device must be selected for
master operation while all other devices must be programmed for slave operation.
Initialization includes the operating mode of the device’s SSC and also the function of
the respective port lines.
Figure 20-4 SSC Full-Duplex Configuration
The data output pins MRST of all slave devices are connected onto one receive line in
this configuration. 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
and enables the driver of its MRST pin. All the other
slaves must program their MRST pins to input. Therefore, only one slave can put its
data onto the master’s receive line. Only reception of 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.
•
The slaves use open drain output on MRST
. This forms a wired-AND connection.
The receive line needs an external pull-up in this case. Corruption of the data on the
receive line sent by the selected slave is avoided when all slaves not selected for
MCA05779
MTSR
MRST
CLK
Clock
Shift Register
Device #2
Slave
MTSR
MRST
CLK
Clock
Shift Register
Device #1
Master
MTSR
MRST
CLK
Clock
Shift Register
Device #3
Slave
Clock
Receive
Transmit