
XC161 Derivatives
Peripheral Units (Vol. 2 of 2)
High-Speed Synchronous Serial Interface (SSC)
User’s Manual
19-11
V2.2, 2004-01
SSC_X, V2.0
19.2.3
Half-Duplex Operation
In a Half-Duplex configuration, 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 the
one data exchange line, serial data may be moved between arbitrary stations.
Similar to 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 outputs and send only ones (1s).
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). 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 19-5
SSC Half-Duplex Configuration
Clock
MCA05458
Master
Device #1
Transmit
Clock
MTSR
SCLK
MRST
Shift Register
Clock
MTSR
SCLK
MRST
Shift Register
Clock
Device #2
Slave
MTSR
SCLK
Shift Register
Device #3
Slave
Symbols
Input
Push/Pull Output
Open-Drain Output
Tri-Stated = Input
MRST