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TC1796
Peripheral Units (Vol. 2 of 2)
Synchronous Serial Interface (SSC)
User’s Manual
20-9
V2.0, 2007-07
SSC, V2.1
20.1.2.3 Half-Duplex Operation
The description in this section assumes that the SSC is used with software controlled bi-
directional GPIO port lines that provide open-drain capability (see also
).
In a half-duplex configuration, only one data line is necessary for both receiving
and
transmitting data. The data exchange line is connected to both pins MTSR and MRST of
each device, and the clock line is connected to the SCLK pin.
The master device controls the data transfer by generating the shift clock, while the slave
devices receive it. Due to the fact that all transmit and receive pins are connected to the
one data exchange line, serial data may be moved between arbitrary stations.
As in full-duplex mode, there are two ways to avoid collisions on the data exchange line:
•
Only the transmitting device may enable its transmit pin driver
•
The non-transmitting devices use open-drain output and send only 1’s
Because the data inputs and outputs are connected together, a transmitting device will
clock in its own data at the input pin (MRST for a master device, MTSR for a slave). In
this way, any corruption is detected on the common data exchange line when the
received data is not equal to the transmitted data.