XC886/888CLM
Serial Interfaces
User’s Manual
12-36
V1.3, 2010-02
Serial Interfaces, V 1.0
be prepared via the related ALTSEL register, or the output latch must be loaded
with the clock idle level.
12.3.1.3
Half-Duplex Operation
In a half-duplex mode, only one data line is necessary for both receiving and transmitting
of data. The data exchange line is connected to both the MTSR and MRST pins of each
device, the shift 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 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 ones.
Since 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). By this
method, any corruptions on the common data exchange line are detected if the received
data is not equal to the transmitted data.
Figure 12-14 SSC Half-Duplex Configuration
Master
Device #1
Shift Register
Clock
MTSR
CLK
MRST
MRST
CLK
MTSR
Clock
Shift Register
Device #2
Slave
Common
Transmit/
Receive
Line
Slave
Device #3
MRST
CLK
MTSR
Clock
Shift Register
Transmit
Clock
*
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